LED luminescence apparatus and method of driving the same

ABSTRACT

A light-emitting diode (LED) driving circuit configured to drive LED units includes a rectification circuit unit to receive an alternating current (AC) power voltage and rectify the AC power voltage to output a unidirectional ripple voltage, a pulse-width modulation (PWM) signal generation unit to generate PWM decision signals. The PWM signal generation unit is configured to sequentially drive the LEDs according to the PWM decision signals.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.13/360,477, filed on Jan. 27, 2012, and claims the benefit of U.S.Provisional Patent Application Nos. 61/437,288, filed on Jan. 28, 2011;61/437,296, filed on Jan. 28, 2011; 61/437,932, filed on Jan. 31, 2011;61/438,304, filed on Feb. 1, 2011; 61/438,308, filed on Feb. 1, 2011;61/442,732, filed on Feb. 14, 2011; 61/467,782, filed on Mar. 25, 2011;and 61/565,574, filed on Dec. 1, 2011, which are all hereby incorporatedby reference for all purposes as if fully set forth herein.

BACKGROUND

Field

Exemplary embodiments of the present invention relate to aLight-Emitting Diode (LED) luminescence apparatus using AlternatingCurrent (AC) power and, more particularly, to an LED luminescenceapparatus that is capable of improving power factor and Total HarmonicsDistortion (THD) and effectively dealing with the distortion andcommercial AC voltage and variation in the magnitude thereof. Exemplaryembodiments of the present invention also relate to an LED luminescenceapparatus equipped with a driving circuit, which defines thecharacteristic range of total LED driving voltage (Vf) and uses LEDshaving a plurality of driving voltages, thus decreasing a flickerphenomenon and increasing the quantity of light while minimizing aninterval in which the LEDs are turned off.

Discussion of the Background

FIG. 1 is a block diagram of a conventional LED luminescence apparatususing AC power.

The conventional LED luminescence apparatus using AC power 1 isconfigured to provide unidirectional ripple voltage, output from arectification circuit 2 that is implemented using a bridge circuit, tohigh voltage LEDs 3-1 to 3-4 via a resistor 4.

In such a conventional LED luminescence apparatus using AC power, LEDdriving current provided to the LEDs may not have a complete sinusoidalwave form and there may be a phase difference between the LED drivingcurrent and AC voltage, and therefore a problem may arise in thatelectrical characteristics, including power factor and THD, do notfulfill requirements for LED lighting.

In order to solve this problem, there is a method of reducing LEDdriving voltage (forward voltage: Vf). However, since the drivingefficiency and light output characteristics of high-voltage driven LEDsmay be determined depending on the driving voltage Vf of the LEDs, thesimple reduction in the driving voltage Vf of the LEDs may cause theproblem of not fulfilling the power factor and the THD that arepresented in the LED lighting standard.

Furthermore, commercial AC power may not provide AC voltage in idealsinusoidal wave form. That is, the problem of the magnitude ofcommercial AC voltage being higher or lower than that of a referencevoltage in ideal sinusoidal wave form arises, and the waveform thereofmay be distorted by harmonics.

FIG. 2A and FIG. 2B are waveform diagrams showing the waveforms ofcurrent, each of which is provided to LEDs and is subject to variationin AC power or the distortion of the AC power, in the conventional LEDluminescence apparatus over time.

When the instantaneous voltage of an input voltage exceeds the drivingvoltage Vf of the LEDs, a driving current flows in proportion to theinput voltage. As shown in FIG. 2A and FIG. 2B, the driving current ofLEDs may be distorted by such deformation of the waveform of AC voltage.As a result, when LEDs are driven using AC power, the light emissionefficiency of the LEDs may significantly vary depending on the shape andmagnitude of the driving current.

Further, in order to drive LEDs using AC power, various circuits such asa rectification circuit, a power supply circuit, a voltage detectioncircuit, a pulse generation circuit, a switch circuit, and a currentcontrol circuit may be required.

SUMMARY

Exemplary embodiments of the present invention provide a light-emittingdiode (LED) luminescence apparatus and a method of driving an LEDluminescence apparatus.

Additional features of the invention will be set forth in thedescription which follows, and in part will be apparent from thedescription, or may be learned by practice of the invention.

An exemplary embodiment of the present invention discloses alight-emitting diode (LED) luminescence apparatus, which includes arectification circuit unit to receive an alternating current (AC) powervoltage and rectify the AC power voltage to output a unidirectionalripple voltage, a plurality of LED units connected in series, each ofthe plurality of LED units comprising an anode and a cathode, theplurality of LED units being configured to receive the unidirectionalripple voltage, a plurality of switch units, one end of each beingconnected to the cathode of one of the plurality of LED units, aplurality of constant current control circuit units, one end of eachbeing connected to an another end of a respective switch unit to receivea current from the respective switch unit, each of the constant currentcontrol circuit units being configured to output a current controlsignal to the respective switch unit to control a magnitude of thereceived current to have a specific value, and a current comparison unitto receive currents flowing from the plurality of switching units, andgenerate a plurality of switching control signals for the respectiveswitch units to sequentially drive the plurality of constant currentcontrol circuit units.

Another exemplary embodiment of the present invention discloses a methodof driving an a light-emitting diode (LED) luminescence apparatus, whichincludes applying a rectified alternating current (AC) voltage to aplurality of LED stages, each of the plurality of LED stages comprisingan LED unit, a switch unit connected to the LED unit, and a constantcurrent control circuit unit connected to the switch unit, detecting acurrent from a constant current control circuit at the first LED stage,converting the detected current into a DC current at the first LEDstage, comparing the DC current with a reference current to generate anerror voltage signal based on the comparison result at the first LEDstage, and comparing the error voltage signal with an input voltagesignal to generate a pulse-width modulation (PWM) signal based on thecomparison result at the first LED stage.

Still another exemplary embodiment of the present invention discloses alight-emitting diode (LED) luminescence apparatus, which includes arectification circuit unit to receive an alternating current (AC) powervoltage and rectify the AC power voltage to output a unidirectionalripple voltage, a plurality of LED channel units connected in parallelto receive the unidirectional ripple voltage, and a pulse-widthmodulation (PWM) signal generation unit to generate a plurality of PWMdecision signals. The plurality of LED channel units are configured toreceive the plurality of PWM decision signals from the PWM signalgeneration unit, respectively, and also configured to be sequentiallydriven in response to the plurality of PWM decision signals.

Still another exemplary embodiment of the present invention discloses amethod of driving a light-emitting diode (LED) luminescence apparatus,which includes receiving an alternating current (AC) power voltage,rectifying the AC power voltage to output a unidirectional ripplevoltage, applying the unidirectional ripple voltage to a plurality ofLED channel units, which are connected in parallel, generating aplurality of pulse-width modulation (PWM) decision signals, and applyingthe plurality of PWM decision signals to the plurality of LED channelunits, respectively, to sequentially drive the plurality of LED channelunits.

Still another exemplary embodiment of the present invention discloses alight-emitting diode (LED) luminescence apparatus, which includes arectifier to receive an alternating current (AC) voltage and rectify theAC voltage to generate a rectified voltage, a first LED channel unit anda second LED channel unit connected in parallel to receive the rectifiedvoltage, and a pulse-width modulation (PWM) signal generation unit togenerate a first PWM decision signal and a second PWM signal. The firstand second LED channel units are configured to receive the first PWMdecision signal and the second PWM decision signal, respectively, andthe first and second LED channel units are also configured to besequentially driven in response to the first and second PWM decisionsignals.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory and areintended to provide further explanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this specification, illustrate embodiments of the invention, andtogether with the description serve to explain the principles of theinvention.

FIG. 1 is a block diagram of a conventional LED luminescence apparatususing AC power.

FIG. 2A and FIG. 2B are waveform diagrams showing the waveform ofcurrent in the conventional LED luminescence apparatus of FIG. 1.

FIG. 3 is a block diagram of an LED luminescence apparatus using ACpower according to an exemplary embodiment of the present invention.

FIG. 4 is a waveform diagram illustrating the waveforms of AC voltageand AC current provided to the LEDs in the LED luminescence apparatususing AC power according to the exemplary embodiment of FIG. 3.

FIG. 5 is a waveform diagram illustrating the waveforms of the controlsignals of the switches provided in the LED luminescence apparatus usingAC power according to the exemplary embodiment of FIG. 3.

FIG. 6 is a block diagram of an LED luminescence apparatus using ACpower according to an exemplary embodiment of the present invention.

FIG. 7 is a waveform diagram showing the waveforms of AC voltage andcurrent supplied to LEDs using multi-stage current driving according toan exemplary embodiment of the present invention.

FIG. 8 is a graph showing the number of LEDs versus an LED OFF intervalratio when a plurality of LED units having the same driving voltage areconnected in series in the LED luminescence apparatus using AC poweraccording to an exemplary embodiment of the present invention.

FIG. 9 is a graph showing a relationship between the driving voltage ofa first diode and an OFF interval in the LED luminescence apparatususing AC power according to the exemplary embodiment of FIG. 3.

FIG. 10 is a waveform diagram showing the waveforms of AC voltage and ACcurrent supplied to LEDs in the LED luminescence apparatus using ACpower according to an exemplary embodiment of the present invention.

FIG. 11 is a waveform diagram illustrating waveforms of AC voltage andcurrent provided to LEDs during multi-stage current driving.

FIG. 12 is a block diagram of an LED luminescence apparatus according toan exemplary embodiment of the present invention.

FIG. 13 is a detailed block diagram of the LED luminescence apparatususing AC power based on FIG. 12.

FIG. 14 is a waveform diagram illustrating the waveform of the PWMoutput signal of the average current control circuit unit in the LEDluminescence apparatus using AC power according to the exemplaryembodiment shown in FIG. 13.

FIG. 15 is a waveform diagram showing the waveforms of AC voltage andcurrent supplied to LEDs according to multi-stage Pulse Width Modulation(PWM) current driving.

FIG. 16 is a block diagram showing an LED luminescence apparatusaccording to an exemplary embodiment of the present invention.

FIG. 17 is a detailed block diagram showing LED channels in the LEDluminescence apparatus according to the exemplary embodiment shown inFIG. 16.

FIG. 18 is a waveform diagram showing PWM decision signals obtained byfrequency division in the LED luminescence apparatus according to theexemplary embodiment of the present invention.

FIG. 19 is a detailed block diagram showing PWM control in the LEDluminescence apparatus according to an exemplary embodiment of thepresent invention.

FIG. 20 is a waveform diagram showing the waveforms of LED drivingcurrents depending on PWM output signals in the LED luminescenceapparatus according to the exemplary embodiment shown in FIG. 19.

FIG. 21 is a block diagram of an LED luminescence apparatus according toan exemplary embodiment of the present invention.

FIG. 22A and FIG. 22B are waveform diagrams illustrating LED drivingcurrent waveforms without and with an improved LED OFF interval,respectively, in the LED luminescence apparatus according to anexemplary embodiment shown in FIG. 21.

FIG. 23 is a waveform diagram showing PWM decision signals obtained byfrequency division in the LED luminescence apparatus according to anexemplary embodiment of the present invention.

FIG. 24 is a waveform diagram showing the waveforms of LED drivingcurrents depending on PWM output signals in the LED luminescenceapparatus according to the exemplary embodiment shown in FIG. 23.

FIG. 25 is a block diagram showing an LED driving circuit implemented asan LED driving circuit package according to an exemplary embodiment ofthe present invention.

FIG. 26 is a plan view showing the LED driving circuit package accordingto an exemplary embodiment of the present invention.

FIG. 27 is a side sectional view showing the LED driving circuit packageaccording to the exemplary embodiment shown in FIG. 26.

FIG. 28 is a plan view showing an LED driving circuit package accordingto an exemplary embodiment of the present invention.

FIG. 29 is a side sectional view showing the LED driving circuit packageaccording to the exemplary embodiment shown in FIG. 28.

FIG. 30 and FIG. 31 are plan views showing examples of the arrangementof terminals and the implementation of the rectification unit on the topsurface of the silicon substrate in the LED driving circuit package ofFIG. 28 according to exemplary embodiments of the present invention.

FIG. 32 is a diagram showing the arrangement of electrode pads and theconnection between the electrode pads and LEDs in the LED drivingcircuit package according to an exemplary embodiment of the presentinvention.

FIG. 33 is a diagram showing the arrangement of electrode pads and theconnection between the electrode pads and a heat dissipation pad in theLED driving circuit package according to an exemplary embodiment of thepresent invention.

FIG. 34 is a diagram showing an example of a luminescence module towhich the LED driving circuit package according to an exemplaryembodiment of the present invention is applied.

FIG. 35 is a diagram showing an example of an LED chip which can beapplied to the LED luminescence apparatus of the present inventiondescribed above with respect to FIG. 3, FIG. 4, FIG. 5, and FIG. 6.

FIG. 36 is a plan view showing an LED package using the multi-cell LEDchip shown in FIG. 35.

FIG. 37A and FIG. 37B are diagrams showing an exemplary embodiment of anLED package which can be applied to the LED luminescence apparatusaccording to exemplary embodiment shown in FIG. 35 and FIG. 36.

FIG. 38A and FIG. 38B are diagrams showing an exemplary embodiment of anLED package which can be applied to the LED luminescence apparatus shownin FIG. 35 and FIG. 36.

FIG. 39 is a waveform diagram illustrating an OFF interval of AC currentprovided to LEDs, in the LED luminescence apparatus using AC poweraccording to the exemplary embodiment described with respect to FIG. 3.

FIG. 40 is a block diagram of an LED luminescence apparatus using ACpower according to an exemplary embodiment of the present invention.

FIG. 41 is a waveform diagram illustrating waveforms of AC voltage andAC current, which are provided to LEDs, in the LED luminescenceapparatus using AC power according to the exemplary embodiment of FIG.40.

FIG. 42 is a waveform diagram illustrating waveforms of control signalsof switches provided in the LED luminescence apparatus using AC poweraccording to the exemplary embodiment of FIG. 40, a waveform of currentflowing through the switches, and a waveform of current provided to LEDsover time.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

The invention is described more fully hereinafter with reference to theaccompanying drawings, in which exemplary embodiments of the inventionare shown. This invention may, however, be embodied in many differentforms and should not be construed as limited to the exemplaryembodiments set forth herein. Rather, these exemplary embodiments areprovided so that this disclosure is thorough, and will fully convey thescope of the invention to those skilled in the art. In the drawings, thesize and relative sizes of layers and regions may be exaggerated forclarity. Like reference numerals in the drawings denote like elements.

It will be understood that when an element or layer is referred to asbeing “on” or “connected to” another element or layer, it can bedirectly on or directly connected to the other element or layer, orintervening elements or layers may be present. In contrast, when anelement is referred to as being “directly on” or “directly connected to”another element or layer, there are no intervening elements or layerspresent.

FIG. 3 is a block diagram of an LED luminescence apparatus using ACpower according to an exemplary embodiment of the present invention.

Referring to FIG. 3, the LED luminescence apparatus using AC poweraccording to the present exemplary embodiment may include an AC powersource 11, a rectification circuit unit 12, a plurality of LED units13-1 to 13-N, a plurality of switches 14-1 to 14-(N−1), constant currentcontrol circuit units 15-1 to 15-(N−1), and a current comparison unit16.

The AC power source 11 may be a commercial AC power source, and mayprovide AC voltage in a sinusoidal wave form.

The rectification circuit unit 12 may generate unidirectional ripplevoltage by rectifying AC voltage provided by the AC power source 11. Therectification circuit unit 12 may be a bridge circuit that isimplemented using a plurality of diodes.

The plurality of LED units 13-1 to 13-N may be connected in series toeach other in forward direction. That is, one terminal of therectification circuit unit 12 is connected to an anode, a positiveterminal, of the LED unit 13-1, and a cathode, a negative terminal, ofthe LED unit 13-1 is connected to an anode of the LED unit 13-2. Acathode of the LED unit 13-2 is connected to an anode of the LED unit13-3, and so on. Each of the LED units 13-1 to 13-N shown in FIG. 3 maybe a single LED, or may include a plurality of LEDs, the same polarityterminals of which are connected to each other (that is, which areconnected in parallel to each other). Here, the number of LEDs that areconnected in series may be increased to improve the efficiency of adrive circuit and perform current control in multiple stages.

Each of the switches 14-1 to 14-(N−1) may be connected, at one endthereof, to a node where two of the plurality of LED units 13-1 to 13-Nare connected to each other. That is, a first switch 14-1 may beconnected to a node where a first LED unit 13-1 and a second LED unit13-2 are connected to each other, and a second switch 14-2 may beconnected between the second LED unit 13-2 and a third LED unit 13-3. An(N−1)th switch 14-(N−1) may be connected between an (N−1)th LED unit13-(N−1) and an Nth LED unit 13-N.

These switches 14-1 to 14-(N−1) may operate in response to switchcontrol signals S1 to SN output from the current comparison unit 16,which will be described later. Furthermore, the switches 14-1 to 14-Nmay operate in response to control signals from the constant currentcontrol circuit units 15-1 to 15-N.

The constant current control circuit units 15-1 to 15-N may controlcurrent flowing through the plurality of LED units 13-1 to 13-N so thatit has a specific magnitude. The constant current control circuit units15-1 to 15-(N−1) may be connected to the remaining ends of the switches14-1 to 14-N.

The current comparison unit 16 may receive currents i2 to iN flowingthrough the switches 14-2 to 14-N in response to opening of the switches14-2 to 14-N, which is respectively controlled by the constant currentcontrol circuit units 15-1 to 15-N. In greater detail, the currentcomparison unit 16 generates switching control signals S1 to SN to close(turn on) the switches 14-1 to 14-N or open (turn off) so that theconstant current control circuit units 15-1 to 15-N sequentiallyoperate. That is, each of the switching control signals S1 to SNswitches a corresponding switch 14-1 to 14-N to an open state(turned-off state) when downstream stage currents i2 to iN are receivedand if any one thereof reaches a preset value. For example, the firstswitching control signal S1 switches the first switch 14-1 to an openstate when the downstream stage currents i2 to iN are received and ifany one thereof reaches the preset value, the second switching controlsignal S2 switches the second switch 14-2 to an open state (turned-offstate) when the downstream stage currents i3 to iN are received and ifany one thereof reaches the preset value, and the (N−1)th switch controlsignal S(N−1) switches the (N−1)th switch 14-(N−1) to an open state(turned-off state) when the downstream current iN is received and if thecorresponding current reaches the preset value.

The operation of the LED luminescence apparatus using AC power accordingto the present exemplary embodiment shown in FIG. 3 will now bedescribed in detail.

First, when AC voltage is applied to the rectification circuit unit 12by the AC power source 11, the rectification circuit unit 12 rectifiesthe AC voltage, and then outputs unidirectional ripple voltage. As shownin FIG. 3, the output voltage of the AC power source 11, that is,voltage input to the rectification circuit unit 12, is AC voltagealternating between positive and negative voltage levels, and thevoltage output from the rectification circuit unit 12 assumes the formof unidirectional ripple voltage in which the negative direction ofvoltage has been switched to a positive direction. The ripple voltage isprovided to the plurality of LED units 13-1 to 13-N.

Thereafter, as ripple voltage increases, the LED units 13-1 to 13-N cansequentially emit light. Such light emitting operation of the LED unitswill now be described with reference to FIGS. 4 and 5.

FIG. 4 is a waveform diagram illustrating the waveforms of AC voltageand AC current provided to the LEDs in the LED luminescence apparatususing AC power according to the present exemplary embodiment.

Furthermore, FIG. 5 is a waveform diagram illustrating the waveforms ofthe control signals of the switches provided in the LED luminescenceapparatus using AC power according to the present exemplary embodiment,the waveform of current flowing through the switches, and the waveformof current provided to the LEDs over time.

FIGS. 4 and 5 illustrate the case where the number of LED units is four,that is, N=4. Accordingly, an example of the case where in FIG. 3, thevalue of N is set to four will be described. Furthermore, FIGS. 4 and 5illustrate only a single cycle of ripple voltage provided by therectification circuit unit 12. Since the same operation is performed inthe remaining cycles of the ripple voltage, description of the remainingcycles is omitted for the sake of brevity.

When the magnitude of the ripple voltage provided to the LED units 13-1to 13-4 increases and the ripple voltage reaches the driving voltage(forward voltage Vf1) of the first LED unit 13-1, current flows throughthe first LED unit 13-1 and light is emitted (at time t0 of FIGS. 4 and5)

Here, the first switch 14-1 to the fourth switch 14-4 are initially setto a close state (turned-on state). Such input voltage Vf1 is thevoltage which enables the first LED unit 13-1 to be turned on, and thecurrent corresponding to the input voltage Vf1 flows through a path tothe first constant current control circuit unit 15-1 via the first LEDunit 13-1. In this case, the first switch 14-1 uniformly controlscurrent passing through the first constant current control circuit unit15-1 in response to a control signal output from the first constantcurrent control circuit unit 15-1. The first constant current controlcircuit unit 15-1 performs constant current control so that referencecurrent preset to drive the first LED unit 13-1 can flow through thefirst LED unit 13-1. The operation in which the first LED unit 13-1initiates light emission corresponds to a time interval t0-t1 in FIGS. 4and 5.

Thereafter, when the magnitude of the ripple voltage further increasesand voltage applied to the second LED unit 13-2 reaches the drivingvoltage of the second LED unit 13-2 (when the magnitude of the ripplevoltage becomes Vf2), current flows through the second LED unit 13-2 andthe second LED unit 13-2 emits light (at time t1 of FIGS. 4 and 5).Here, the input voltage Vf2 is the voltage which enables the first andsecond LED units 13-1 and 13-2 to be turned on, and the currentcorresponding to the input voltage Vf2 flows through a path to thesecond constant current control circuit unit 15-2 via the second LEDunit 13-2. In this case, the current comparison unit 16 senses that thecurrent i2 of the second constant current control circuit unit 15-2 is apreset value, generates a first switching control signal S1, thusopening (turning off) the first switch 14-1. At the same time, thesecond switch 14-2 performs control in response to the control signaloutput from the second constant current control circuit unit 15-2 sothat current flowing through the second constant current control circuitunit 15-2 becomes the reference current preset to drive both the firstand second LED units 13-1 and 13-2.

Using this operation, control may be performed such that constantcurrent flows through the first LED unit 13-1 and the second LED unit13-2. Furthermore, as shown in FIGS. 4 and 5, at time t1, the firstswitch 14-1 is turned off, and stepped input current can be formed bythe constant current control of the second constant current controlcircuit unit 15-2.

Similarly to the above-described procedure, when the ripple voltagefurther increases and voltage applied to the third LED unit 13-3 becomesthe driving voltage of the third LED unit 13-3 (when the magnitude ofthe ripple voltage becomes Vf3), current flows through the third LEDunit 13-3 and then the third LED unit 13-3 emits light (at time t2 ofFIGS. 4 and 5). Here, the input voltage Vf3 is the voltage which enablesthe first LED unit 13-1 to the third LED unit 13-3 to be turned on, andcurrent corresponding to the input voltage Vf3 flows through a path tothe third constant current control circuit unit 15-3 via the third LEDunit 13-3. In this case, the current comparison unit 16 senses that thecurrent i3 of the third constant current control circuit unit 15-3 is apreset value, and generates a second switching control signal S2, thusopening (turning off) the second switch 14-2. The first switch controlsignal S1 is maintained in its previous state, so that the first switch14-1 is maintained in an open (turned-off) state. At the same time, thethird switch 14-3 performs control in response to a control signaloutput from the third constant current control circuit unit 15-3 so thatcurrent flowing through the third constant current control circuit unit15-3 becomes the reference current preset to drive the first to thirdLED units 13-1 to 13-3.

Using this operation, control may be performed such that constantcurrent flows through the first LED unit 13-1, the second LED unit 13-2,and the third LED unit 13-3. Furthermore, as shown in FIGS. 4 and 5, attime t2, the first switch 14-1 and the second switch 14-2 are turnedoff, and stepped input current can be formed by the constant currentcontrol of the third constant current control circuit unit 15-3.

Similarly to the above-described procedure, when the ripple voltagefurther increases, and voltage applied to the fourth LED unit 13-4becomes the driving voltage of the fourth LED unit 13-4 (when themagnitude of the ripple voltage becomes Vf4), current flows through thefourth LED unit 13-4 and then the fourth LED unit 13-4 emits light (attime t3 of FIGS. 4 and 5). Here, the input voltage Vf4 is the voltagewhich enables all of the first LED unit 13-1 to the fourth LED unit 13-4to be turned on, and current corresponding to the input voltage Vf4flows through a path to the fourth constant current control circuit unit15-4 via the fourth LED unit 13-4. In this case, the current comparisonunit 16 senses that the current i4 of the fourth constant currentcontrol circuit unit 15-4 is a preset value, and generates a thirdswitching control signal S3, thus opening (turning off) the third switch14-3. The first and second switch control signals S1 and S2 aremaintained in their previous states, so that the first and secondswitches 14-1 and 14-2 are maintained in an open (turned-off) state. Atthe same time, the fourth switch 14-4 performs control in response to acontrol signal output from the fourth constant current control circuitunit 15-4 so that current flowing through the fourth constant currentcontrol circuit unit 15-4 becomes reference current preset to drive thefirst to fourth LED units 13-1 to 13-4.

Using this operation, control may be performed such that constantcurrent flows through the first LED unit 13-1, the second LED unit 13-2,the third LED unit 13-3, and the fourth LED unit 13-4. Furthermore, asshown in FIGS. 4 and 5, at time t3, the third switch is turned off, andstepped input current can be formed by the constant current control ofthe fourth constant current control circuit unit 15-4.

When ripple voltage passes over a peak and gradually decreases, the LEDunits are sequentially turned off in the sequence from the fourth LEDunit 13-4 to the first LED unit 13-1. When the fourth LED unit 13-4 isturned off (at time t4), the current comparison unit 16 senses that thecurrent i4 of the fourth constant current control circuit unit 15-4 isnot the preset value, and inverts the fourth switching control signalS4, thus closing (turning on) the third switch 14-3. In this case, thefirst and second switching control signals S1 and S2 are maintained intheir previous states, so that the first and second switches 14-1 and14-2 are maintained in an open (turned-off) state. At the same time, thethird switch 14-3 initiates constant current control in response to acontrol signal output from the third constant current control circuitunit 15-3 so that the current flowing through the third constant currentcontrol circuit unit 15-3 is maintained at the reference current presetto drive the first to third LED units 13-1 to 13-3.

A subsequent current control operation is performed in the reverse orderof the constant current control performed during the above-describedinterval t0 to t3, and thus a detailed description thereof will beomitted here.

Although the present exemplary embodiment has been described such thatLED driving current is increased or decreased in stepped form bymulti-stage constant current control, the present invention is notlimited thereto, but the waveform of the LED driving current can bechanged by variously setting reference current for constant currentcontrol.

FIG. 6 is a block diagram of an LED luminescence apparatus using ACpower according to an exemplary embodiment of the present invention.

Since the configuration of the LED luminescence apparatus of theexemplary embodiment shown in FIG. 6 is the same as that of theexemplary embodiment described above with respect to FIG. 3, except forthe LED units 13-1-1 to 13-N-M, a description thereof will be omittedhere.

In the present exemplary embodiment, each of the LED units is configuredsuch that a plurality of LEDs is connected in parallel to each other,for example, a first LED unit 13-1-1 to 13-1-M is configured such that MLEDs are connected in parallel to each other. Here, the number of LEDsconnected in parallel may be increased for the purpose of an increase inthe luminous flux of an LED lighting lamp or an increase in thecapability of the lamp.

As described above, exemplary embodiments of the present invention areconfigured to sequentially drive the series-connected LEDs at constantcurrent using AC voltage, so that current that increases or decreases instepped form can be provided, as shown in FIGS. 4 and 5, and thereforeLED driving current approximate to a sinusoidal wave equal to AC voltageis provided, thereby enabling problems related to the power factor, THD,etc. to be solved.

Constant driving current can be provided in the event of a variation inAC voltage (distortion, or an increase or decrease in the magnitude ofvoltage) by controlling current so that it has a constant value at eachstage, thereby improving the light output efficiency of AC-driven LEDs.

A method of generating the driving current of an LED in a stepped shapeusing multi-stage current driving is shown in FIG. 7.

FIG. 7 is a waveform diagram showing the waveforms of AC voltage andcurrent supplied to an LED according to multi-stage current driving.

As shown in FIG. 7, before a predetermined voltage is applied to an LED,the LED is maintained in an OFF state. Accordingly, before the inputvoltage reaches the turn-on voltage of the LED, there exists an LED OFFinterval in which input current is not present. Due to suchcurrent-voltage operating characteristics, the power factor defined asthe ratio of input real power to input apparent power may bedeteriorated and a harmonic component may increase. In this case, theLED OFF interval occurs depending on the characteristics of the drivingvoltage (Vf) of the LED, which may result in a flicker phenomenon,deteriorated power factor, and decreased quantity of light, depending onthe size of the LED OFF interval.

As shown in FIG. 7, there is an OFF interval during which current doesnot flow between the time at which a plurality of LED units aresequentially turned on and then sequentially turned off in one cycle ofthe ripple voltage, and the time at which the LED units are turned onagain in a subsequent cycle of the ripple voltage. When this OFFinterval increases, the power factor (defined as the ratio of input realpower to input apparent power) may decrease, and a harmonic componentmay increase, and thus it is preferable to minimize such an OFFinterval.

There is a relationship between the driving voltage (forward voltage:Vf) of LED units employed in the luminescence apparatus and the OFFinterval, thus the driving voltage may be manipulated in order tominimize the OFF interval.

Hereinafter, techniques for minimizing the OFF interval according toexemplary embodiments of the present invention will be described withrespect to FIG. 8, FIG. 9, and FIG. 10, using various graphs showingrelationships between the driving voltage of the LED units and the OFFinterval.

FIG. 8 is a graph showing the number of LEDs versus an OFF intervalpercentage when a plurality of LED units having the same driving voltageare connected in series to each other in the LED luminescence apparatususing AC power according to an exemplary embodiment of the presentinvention.

As shown in FIG. 8, when there are a large number of series-connectedLEDs, the percentage of LEDs in the OFF interval may decrease. Inparticular, when the total LED driving voltage Vf is constant, if thenumber of LEDs increases, the driving voltage Vf of each individual LEDdecreases.

Therefore, the percentage of LEDs in the OFF interval may be reduced byemploying LEDs having different driving voltages Vf rather thanemploying LED units having the same driving voltage.

FIG. 9 is a graph showing the relationship between the driving voltageof a first LED unit, which first emits light, and an OFF interval in theLED luminescence apparatus using AC power according to the presentexemplary embodiment and the LED luminescence apparatus described abovewith respect to FIG. 3.

As shown in FIG. 9, it can be seen that as the driving voltage Vf of thefirst LED unit LED1 (13-1 in FIG. 3) which first emits light decreases,the percentage of LEDs in the OFF interval decreases. That is, in thecase of the first LED unit LED1 (13-1) that is turned on when ripplevoltage increases above a threshold voltage and is turned off when theripple voltage decreases below a threshold voltage, since the drivingvoltage Vf is lower for one cycle of the ripple voltage, the first LEDunit may be turned on earlier and may be turned off later. Therefore,when the driving voltage Vf of the first LED unit LED1 (13-1) isdecreased, the OFF interval between the present cycle and a subsequentcycle of the ripple voltage can be reduced.

FIG. 10 is a waveform diagram showing the waveforms of AC voltage and ACcurrent supplied to LEDs in the LED luminescence apparatus using ACpower according to the present exemplary embodiment.

When the number of LED units is four, that is, N=4, the driving voltagesVf1 to Vf4 of the LED units 13-1 to 13-4 (LED1 to LED4) are implementedas different voltages, in particular, in such a way that the drivingvoltage Vf1 of the first LED unit 13-1 (LED1) closest to a rectificationcircuit unit 12 is set to the smallest value, as shown in FIG. 10.Accordingly, compared to FIG. 7, the time point at which the first LEDunit 13-1 (LED1) is turned on is decreased, and the time point at whichthe first LED unit is turned off is increased, thus enabling the turn-onduration of the first LED unit 13-1 (LED1) to be maximized. As a result,the LED OFF interval may be reduced compared to that of the LEDluminescence apparatus shown in FIG. 7.

Meanwhile, although the present exemplary embodiment has been describedsuch that different stepped driving currents are used to drive the LEDunits at respective steps, the present invention is not limited theretoand can be implemented in various forms. For example, the LED units canbe driven using the same current so that variations in the quantity oflight depending on the voltages of LED units having a plurality ofdriving voltages Vf can be minimized. In this case, the driving currentapplied to the LED units can be formed in the shape of a single squarewave.

That is, referring to FIG. 8, FIG. 9, and FIG. 10, the driving voltageof the first LED unit 13-1 (LED1) which is turned on first is set to thelowest voltage and that LED units having different driving voltages Vfmay be used together in FIG. 3, thus minimizing the size of the OFFinterval.

FIG. 6 is a block diagram showing an LED luminescence apparatus using ACpower according to an exemplary embodiment of the present invention.

Since the construction of the LED luminescence apparatus of FIG. 6 issubstantially similar to that of the exemplary embodiment describedabove with respect to FIG. 3, except for LED units 13-1-1 to 13-N-M, adetailed description thereof will be omitted.

In the present exemplary embodiment, each LED unit is implemented usinga plurality of LEDs connected in parallel to each other. For example, afirst LED unit 13-1-1 to 13-1-M can be implemented using Mparallel-connected LEDs. In this case, the number of parallel-connectedLEDs can be increased for the purpose of increasing the luminous flux ofan LED luminescence lamp or increasing the capacity of the lamp.

As described above, the exemplary embodiments of the present inventionare configured such that the driving voltages Vf of LED units may have aplurality of different values, thus reducing an OFF interval compared tothe arrangement of LED units having the same driving voltage accordingto the conventional embodiment. By way of this configuration, theexemplary embodiments of the present invention not only may reduce aflicker phenomenon and increase the quantity of light, but also mayimprove the power factor and reduce the influence of harmonics.

A method of generating LED driving current in a stepped form usingmulti-stage current driving is described below with respect to FIG. 11.

FIG. 11 is a waveform diagram illustrating waveforms of AC voltage andcurrent provided to LEDs during multi-stage current driving.

As shown in FIG. 11, when LED driving current is generated in a steppedform, the LED driving current can be kept constant in the same intervaleven while AC voltage is varying.

However, as AC voltage increases or decreases, an LED driving voltage Vfmay instantaneously vary. As shown in FIG. 11, when an input voltageincreases above a reference voltage, the time at which the input voltagereaches the LED driving voltage is earlier than that for the referenceAC voltage and the time at which the LEDs are turned off is increased.Accordingly, an LED driving interval, that is, an LED current conductioninterval, increases, and therefore the total amount of currentincreases. In contrast, when the input voltage decreases below thereference voltage, the time at which the input voltage reaches the LEDdriving voltage is later than that for the reference AC voltage and thetime at which the LEDs are turned off is decreased. Accordingly, an LEDdriving interval, that is, an LED current conduction interval,decreases, and therefore the total amount of current decreases. As aresult, the multi-stage current control method, such as that describedabove with respect to FIG. 3, may have a varying average LED drivingcurrent depending on variations in AC voltage.

FIG. 12 is a block diagram of an LED luminescence apparatus according toan exemplary embodiment of the present invention.

Referring to FIG. 12, the LED luminescence apparatus according to thepresent exemplary embodiment may include an AC power source 11, arectification circuit unit 12, a plurality of LED units 13-1 to 13-4, aplurality of switches 14-1 to 14-4, constant current control circuitunits 15-1 to 15-4, a current comparison unit 16, average currentcontrol circuit units 18-1 to 18-4, and a signal generation unit 19.

The AC power source 11 may be a commercial AC power source, and mayprovide AC voltage in a sinusoidal wave form.

The rectification circuit unit 12 may generate unidirectional ripplevoltage by rectifying AC voltage provided by the AC power source 11. Therectification circuit unit 12 may be a bridge circuit that isimplemented using a plurality of diodes.

The plurality of LED units 13-1 to 13-4 may be connected in series toeach other. Each of the LED units 13-1 to 13-4 shown in FIG. 3 may be asingle LED, or may include a plurality of LEDs, the same polarityterminals of which are connected to each other (that is, which areconnected in parallel to each other). Here, the number of LEDs that areconnected in series may be increased to improve the efficiency of adrive circuit and perform current control in multiple stages, and thenumber of LEDs that are connected in parallel may be increased toincrease the luminous flux of the LED lighting lamp or the capacity ofthe LED lighting lamp.

For convenience of description, the plurality of LED units 13-1 to 13-4that are connected in series to each other is labeled a first LED unit,a second LED unit, a third LED unit, and a fourth LED unit in thesequence of the connection thereof.

Each of the switches 14-1 to 14-4 may be connected, at one end thereof,to a node where two of the plurality of LED units 13-1 to 13-4 areconnected to each other. That is, a first switch 14-1 may be connectedto a node where a first LED unit 13-1 and a second LED unit 13-2 areconnected to each other, a second switch 14-2 may be connected to a nodewhere the second LED unit 13-2 and a third LED unit 13-3 are connectedto each other, and a third switch 14-3 may be connected to a node wherea third LED unit 13-3 and a fourth LED unit 13-4 are connected to eachother.

These switches 14-1 to 14-4 may operate in response to switch controlsignals S1 to S4 output from the current comparison unit 16, which willbe described later. Furthermore, the switches 14-1 to 14-4 may operatein response to control signals from the constant current control circuitunits 15-1 to 15-4.

The constant current control circuit units 15-1 to 15-4 may controlcurrent flowing through the plurality of LED units 13-1 to 13-4 so thatit has a specific magnitude. The constant current control circuit units15-1 to 15-4 may be connected to the remaining ends of the switches 14-1to 14-4.

The constant current control circuit units 15-1 to 15-4 generate theswitch control signals of switch units 10-1 to 10-4 (see FIG. 13) thatinclude the switches 14-1 to 14-4, and generate a control signal Vgs soas to control the maximum current, as will be described below.

The current comparison unit 16 may receive currents i2 to i4 flowingthrough the switches 14-2 to 14-4 in response to the constant currentcontrol circuit units 15-1 to 15-4, and generate the switching controlsignals S1 to S4 of the switches 14-1 to 14-4. In greater detail, thecurrent comparison unit 16 generates switching control signals S1 to S4depending on the closing (turning on) or opening (turning off) of theswitches 14-1 to 14-4 so that the constant current control circuit units15-1 to 15-4 sequentially operate. That is, each of the switchingcontrol signals S1 to S4 switches a corresponding switch 14-1 to 14-4 toan open state (turned-off state) when downstream stage currents i2 to i4are received and if any one thereof reaches a preset value. For example,the first switching control signal S1 switches the first switch 14-1 toan open state when the downstream stage currents i2 to i4 are receivedand if any one thereof reaches the preset value, the second switchingcontrol signal S2 switches the second switch 14-2 to an open state(turned-off state) when the downstream stage currents i3 to i4 arereceived and if any one thereof reaches the preset value, and the thirdswitch control signal S3 switches the third switch 14-3 to an open state(turned-off state) when the downstream current i4 is received and if thecorresponding current reaches the preset value.

The average current control circuit units 18-1 to 18-4 generate aPulse-Width Modulation (PWM) signal so as to control the average valueof current flowing through the switches 14-1 to 14-4. The averagecurrent control circuit units 18-1 to 18-4 may detect the current of theconstant current control circuit units 15-1 to 15-4 and control theaverage value of driving current flowing through the LED units 13-1 to13-4, regardless of AC power. For example, when the AC voltage is avoltage higher than a higher reference voltage level, the driving timeof the corresponding switches 14-1 to 14-4 is decreased by reducing theduty of the PWM signal, so as to decrease the driving interval of theLED units 13-1 to 13-4. In contrast, when the AC voltage is lowervoltage than a lower reference voltage level, the driving time of thecorresponding switch 14-1 to 14-4 is increased by increasing the duty ofthe PWM signal, so as to increase the driving interval of the LED units13-1 to 13-4.

Meanwhile, since the average current control circuit units 18-1 to 18-4drive the switches 14-1 to 14-4 using a PWM signal, the LED drivingcurrent at each stage is generated in the form of pulse waves.

The signal generation unit 19 generates a ramp signal, and applies it tothe average current control circuit units 18-1 to 18-4 to generate thePWM signal. Here, the frequency of the generated signal is determineddepending on the average driving current of the LED units 13-1 to 13-4,and may be, for example, in the range of 1 KHz to 100 KHz.

The operation of the LED luminescence apparatus using AC power accordingto an exemplary embodiment of the present invention shown in FIG. 12will now be described in detail. Description of the present exemplaryembodiment that substantially overlaps the description provided abovewith respect to FIG. 3 is omitted for the sake of brevity. In FIG. 12,the ripple voltage is provided to the plurality of LED units 13-1 to13-4. Thereafter, as ripple voltage increases, the LED units 13-1 to13-4 sequentially emit light. Such light emitting operation of the LEDunits are described with reference to both FIG. 4 and FIG. 5.

The first average current control circuit unit 18-1 detects the currentof the first constant current control circuit unit 15-1, generates a PWMsignal based on an error with respect to the reference current, anddrives the first switch 14-1. That is, if the actual current is greaterthan or less than the reference current, the duty of the PWM signal isvaried. Accordingly, as shown in FIG. 5, in a time interval t0-t1, thedriving current of the first LED unit 13-1 is generated in a pulse waveform corresponding to that of the PWM signal, with the peak currentthereof being kept constant.

The second average current control circuit unit 18-2 detects the currentof the second constant current control circuit unit 15-2, generates aPWM signal based on an error with respect to the reference current, anddrives the second switch 14-2. Accordingly, as shown in FIG. 5, in atime interval t1-t2, the driving currents of the first LED unit 13-1 andthe second LED unit 13-2 are generated in a pulse wave formcorresponding to that of the PWM signal, with the peak current thereofbeing kept constant.

The third average current control circuit unit 18-3 detects the currentof the third constant current control circuit unit 15-3, generates a PWMsignal based on an error with respect to the reference current, anddrives the third switch 14-3. Accordingly, as shown in FIG. 5, in a timeinterval t2-t3, the driving current of the first to third LED units 13-1to 13-3 is generated in a pulse wave form corresponding to that the PWMsignal, with the peak current thereof being kept constant.

The fourth average current control circuit unit 18-4 detects the currentof the fourth constant current control circuit unit 15-4, generates aPWM signal based on an error with respect to the reference current, anddrives the fourth switch 14-4. Accordingly, as shown in FIG. 5, in atime interval t3-t4, the driving current of the first to fourth LEDunits 13-1 to 13-4 is generated in a pulse wave form corresponding tothat of the PWM signal, with the peak current thereof being keptconstant.

When ripple voltage passes over a peak and gradually decreases, the LEDunits are sequentially turned off in the sequence from the fourth LEDunit 13-4 to the first LED unit 13-1. When the fourth LED unit 13-4 isturned off (at time t4), the current comparison unit 16 senses that thecurrent i4 of the fourth constant current control circuit unit 15-4 isnot the preset value, and inverts the third switching control signal S3,thus closing (turning on) the third switch 14-3. In this case, the firstand second switching control signals S1 and S2 are maintained in theirprevious states, so that the first and second switches 14-1 and 14-2 aremaintained in an open (turned-off) state. At the same time, current isinput to the third constant current control circuit unit 15-3, andconstant current control is initiated such that the reference currentpreset to drive the first to third LED units 13-1 to 13-3 can bemaintained.

The third average current control circuit unit 18-3 detects the currentof the third constant current control circuit unit 15-3, generates a PWMsignal based on an error with respect to the reference current, anddrives the third switch 14-3. Accordingly, as shown in FIG. 5, in a timeinterval t4-t5, the driving current of the first to third LED units 13-1to 13-3 is generated in a pulse wave form corresponding to that the PWMsignal, with the peak current thereof being kept constant.

A subsequent current control operation is performed in the reverse orderof the constant current control performed during the above-describedinterval t0 to t3, and thus a detailed description thereof will beomitted here.

Referring to FIG. 13 and FIG. 14, the control of the peak current andaverage current of LED driving current will be described in detailbelow.

FIG. 13 is a detailed block diagram of the LED luminescence apparatususing AC power based on FIG. 12.

In FIG. 13, switch units 10-1 to 10-4 correspond to the switches 14-1 to14-4 of FIG. 12, and each include switching devices Q1 to Q4 andresistors Rg1 to Rg4, and the control signals of the constant currentcontrol circuit units 15-1 to 15-4 are input to the gates g1 to g4 ofthe switching devices Q1 to Q4. The switch units 10-1 to 10-4 generateconstant current that fulfills the driving voltages Vf1 to Vf4 of theLED units 13-1 to 13-4.

The constant current control circuit units 15-1 to 15-4 are connected tothe sources s1 to s4 and gates g1 to g4 of the switching devices Q1 toQ4. Furthermore, the constant current control circuit units 15-1 to 15-4control the switching devices Q1 to Q4, which include powersemiconductors, such as field effect transistors (FETs) or bipolarjunction transistors (BJTs), at linear regions. That is, the constantcurrent control circuit units 15-1 to 15-4 generate signals that controlVgs of the switching devices Q1 to Q4 so that the driving current of theLED unit 13-1 fulfills a set peak current value. In this case, theswitching devices Q1 to Q4 operate at linear regions. Specifically, eachof the constant current control circuit units 15-1 to 15-4 senses thecurrent flowing from the respective switching device Q1 to Q4 via therespective resistors R1 to R4, and generates a control signal to controlthe respective switching device Q1 to Q4 based on the amount of thesensed current. For this, each of the constant current control circuitunits 15-1 to 15-4 may include a switching element (not shown) which isselectively turned on according to the sensed current. Such switchingelement may be power semiconductors, such as field effect transistors(FETs) or bipolar junction transistors (BJTs). That is, if the switchingelement is a BJT, a base terminal of the BJT is connected to the sources1 of the respective switching device Q1 to Q4, a collector terminal ofthe BJT is connected to a gate terminal g1 of the respective switchingdevice Q1 to Q4, and an emitter terminal of the BJT is connected to therespective resistors R1 to R4.

The average current control circuit units 18-1 to 18-4 may be configuredto include detection resistors R1 to R4 for detecting the current of theconstant current control circuit units 15-1 to 15-4, current conversionunits 20-1 to 20-4 for converting the detected current into DC current,first comparators 21-1 to 21-4 for performing comparison with referencecurrents Iref1 to Iref4 and outputting error values, and secondcomparators 22-1 to 22-4 for comparing the error values of the firstcomparators 21-1 to 21-4 with the signal Vramp of the signal generationunit 19 and generating PWM signals.

Here, the detection resistors R1 to R4 are connected in series to theconstant current control circuit units 15-1 to 15-4, and the currentconversion units 20-1 to 20-4 are connected between the detectionresistors R1 to R4 and the constant current control circuit units 15-1to 15-4, and the current flowing from the constant current controlcircuit units 15-1 to 15-4 is changed to a predetermined level byaveraging the current. For example, each of the current conversion units20-1 to 20-4 may be configured to include a filter.

The outputs of the current conversion units 20-1 to 20-4 are connectedto the negative (−) terminals of the first comparators 21-1 to 21-4, andthe reference currents Iref1 to Iref4 are connected to the positive (+)terminals of the first comparators 21-1 to 21-4. The outputs of thefirst comparators 21-1 to 21-4 are connected to the positive (+)terminals of the second comparators 22-1 to 22-4, and the output Vrampof the signal generator 19 is connected to the negative (−) terminals ofthe second comparators 22-1 to 22-4.

Furthermore, the average current control circuit units 18-1 to 18-4generate signals that control Vgs of the switching devices Q1 to Q4 sothat the driving current of the LED units 13-1 to 13-4 fulfills the setaverage current. In this case, the switching devices Q1 to Q4 operate atswitching ON/OFF intervals.

The operation of the average current control circuit unit will now bedescribed with reference to FIG. 13 and FIG. 14.

FIG. 14 is a waveform diagram illustrating the waveform of the PWMoutput signal of the average current control circuit unit in the LEDluminescence apparatus using AC power according to the present exemplaryembodiment.

Here, since the operation of the average current control circuit units18-1 to 18-4 is the same at individual current intervals, only theoperation at a first interval, that is, time interval t0 to t1, will bedescribed.

First, when the AC voltage is a reference voltage and the detectionresistor R1 detects the current of the constant current control circuitunit 15-1, the current conversion unit 20-1 converts the detectedcurrent into DC current and inputs the DC current to the firstcomparator 21-1. The first comparator 21-1 compares reference currentIref1 with the output signal of the current conversion unit 20-1, andoutputs an error signal corresponding to the error. For example, thefirst comparator 21-1 may output an error signal if the output signal ofthe current conversion unit 20-1 is less than or greater than to thereference current Iref1.

Thereafter, the second comparator 22-1 compares signal Vramp, input bythe signal generation unit 19, with the output of the first comparator21-1, and generates a PWM reference signal for driving the switchingdevice Q1. As shown in FIG. 14, the PWM reference signal has a band from1 KHz to 100 KHz in response to the generated voltage Vramp of thesignal generator 19. Here, the duty of the PWM reference signal isdetermined by the gain of the first comparators 21-1 to 21-4 so as tocompensate for an increase or a decrease in input voltage.

The switching device Q1 performs ON and OFF switching in response to thePWM reference signal of the average current control circuit unit 18-1,so that the driving current of the LED unit 13-1 is generated in theform of pulses having a constant duty.

Furthermore, when the AC voltage is an excessive voltage, the detectedcurrent input to the negative (−) terminal of the first comparator 21-1increases, and the output of the first comparator 21-1 is a signal at alevel lower than that of the reference AC voltage. Accordingly, as shownin FIG. 14, the level of a signal input to the second comparator 22-1decreases, and therefore the second comparator 22-1 generates a PWMsignal having a reduced duty.

Accordingly, the switching device Q1 performs ON and OFF switching inresponse to the PWM signal having a reduced duty, and therefore the dutyof the driving current of the LED unit 13-1 is reduced, therebyrendering it possible to control average current by reducing the drivinginterval of the LED unit 13-1.

Meanwhile, when the AC voltage is a low voltage and the detected currentinput to the negative (−) terminal of the first comparator 21-1 isreduced, the output of the first comparator 21-1 is a signal at a levelhigher than that of reference AC voltage. Accordingly, as shown in FIG.14, since the level of a signal input to the second comparator 22-1increases, the second comparator 22-1 generates a PWM signal having anincreased duty.

Accordingly, the switching device Q1 performs ON and OFF switching inresponse to the PWM signal having an increased duty, and therefore theduty of the driving current of the LED unit 13-1 is increased, therebyrendering it possible to control average current by increasing thedriving interval of the LED unit 13-1.

As described above, the present invention is configured to control theLED driving current using the PWM signal of the average current so thatthe LED driving current can have an average value regardless ofvariations in AC input voltage, thereby keeping the intensity of lightemitted from the LEDs constant.

Furthermore, the present invention is configured to control a constantcurrent control device, such as a BJT or an FET, in a hybrid manner inwhich linear region control and PWM switching have been combinedtogether, the optical efficiency for input power can be increased,thereby mitigating loss in a driving circuit.

FIG. 15 is a waveform diagram showing the waveforms of AC voltage andcurrent supplied to LEDs according to multi-stage Pulse Width Modulation(PWM) current driving.

As shown in FIG. 15, when the driving current of LEDs is formed in astepped shape, the LED driving current may be maintained at a constantlevel during each stepped interval even if AC voltage fluctuates.Further, in spite of variations in AC input voltage, LED driving currentis controlled to have constant mean power using a PWM signal output froma current control circuit unit, so that LEDs can always output aconstant amount of light.

However, as semiconductor elements for power are used as switchingelements driven by such a PWM signal, and these switching elementsperform switching in a high-frequency band, a large amount of noise mayoccur on input power at the time point at which the switching elementsare turned on or off. That is, since the variation in current increasesover time, various types of noise defined as ElectromagneticInterference (EMI) may be caused. In order to cancel such noise, an EMIfilter unit may be separately added, thus increasing cost of the circuitand making it difficult to realize a small size and light weight of apower circuit.

In order to solve this problem, the LED luminescence apparatus of FIG.16 has been proposed.

FIG. 16 is a block diagram showing an LED luminescence apparatusaccording to an exemplary embodiment of the present invention.

FIG. 17 is a detailed block diagram showing LED channels in the LEDluminescence apparatus according to the present exemplary embodiment.

Referring to FIG. 16, the LED luminescence apparatus according to thepresent exemplary embodiment may include an AC power source 11, arectification circuit unit 12, LED channel units 100 to n×100, and a PWMsignal generation unit 30.

The AC power source 11 may by a commercial AC power source capable ofsupplying AC voltage in a sinusoidal wave form.

The rectification circuit unit 12 may generate unidirectional ripplevoltage Vrec by rectifying the AC voltage supplied by the AC powersource 11. The rectification circuit unit 12 may be a bridge circuitimplemented using a plurality of diodes.

The LED channel units 100 to n×100 are connected in parallel to eachother, and may be sequentially operated in response to PWM signals PWM1to PWMn generated by the PWM signal generation unit 30, which will bedescribed later. For example, the LED channel unit 1 100, the LEDchannel unit 2 200, . . . , the LED channel unit n n×100 may besequentially operated. In this case, the LED channel units 100 to n×100are constructed to have the same structure, and will be described indetail below with reference to FIG. 17.

As shown in FIG. 17, the LED channel unit 100 of the LED luminescenceapparatus according to the present exemplary embodiment may include aplurality of LED units 113-1 to 113-4, a plurality of switches Q1 to Q4,constant current control circuit units 115-1 to 115-4, and a currentcontrol circuit unit 118. Here, although the drawing shows four LEDunits, four switches, four constant current control circuit units, andfour current control circuit units, the number is not limited to 4 andany number of components can be provided in adaptation to the efficiencyof driving circuits and multi-stage current control.

The LED units 113-1 to 113-4 may be connected in series to each other. Asingle LED unit shown in FIG. 17 (one of the LED units 113-1 to 113-4)may be a single LED, and may include a plurality of LEDs, the samepolarity terminals of which are mutually connected to each other (thatis, they are connected in parallel to each other). The number ofseries-connected LEDs may be increased so as to improve the efficiencyof driving circuits and perform multi-stage current control, and thenumber of parallel-connected LEDs may be increased to increase theluminous flux of LED luminescence lamps and increase the capacity oflamps.

Each of the switches Q1 to Q4 may be connected, at one end thereof, to anode where two of the plurality of LED units 113-1 to 113-4 areconnected to each other. That is, a first switch Q1 may be connected toa node where a first LED unit 113-1 and a second LED unit 113-2 areconnected to each other, a second switch Q2 may be connected to a nodewhere the second LED unit 113-2 and a third LED unit 113-3 are connectedto each other, and a third switch Q3 may be connected to a node wherethe third LED unit 113-3 and a fourth LED unit 113-4 are connected toeach other.

The switches Q1 to Q4 may operate in response to switch control signalsS1 to SN output from a current control circuit unit 118, which will bedescribed later. Further, the switches Q1 to Q4 may operate in responseto control signals output from the constant current control circuitunits 115-1 to 115-4.

The constant current control circuit units 115-1 to 115-4 may controlcurrent flowing through the plurality of LED units 113-1 to 113-4 sothat it has a predetermined magnitude. The constant current controlcircuit units 115-1 to 115-4 may be connected to the remaining ends ofthe switches Q1 to Q4.

The constant current control circuit units 115-1 to 115-4 generateswitch control signals for the switch units 10-1 to 10-4 implemented asswitches Q1 to Q4, which will be described later, and generate controlsignals Vgs to control the maximum current.

Meanwhile, the switches Q1 to Q4 and the constant current controlcircuit units 115-1 to 115-4 constitute constant current control units110-1 to 110-4. In more detail, the control signals from the constantcurrent control circuit units 115-1 to 115-4 are applied to the gates g1to g4 of the respective switches Q1 to Q4. The constant current controlunits 110-1 to 110-4 generate constant currents satisfying the drivingvoltages Vf1 to Vf4 of the respective LED units 113-1 to 113-4.

The constant current control circuit units 115-1 to 115-4 are connectedto the sources s1 to s4 and the gates g1 to g4 of the respectiveswitches Q1 to Q4. Further, the constant current control circuit units115-1 to 115-4 perform control such that the switches Q1 to Q4implemented using power semiconductor elements, such as Field EffectTransistors (FET) or Bipolar Junction Transistors (BJT), are operated ina linear region. That is, the constant current control circuit units115-1 to 115-4 generate signals for controlling Vgs of the switches Q1to Q4 so that the driving currents of the LED units 113-1 to 113-4satisfy set peak currents.

The current control circuit unit 118 may receive currents flowingthrough the switches Q2 to Q4 via the constant current control circuitunits 115-1 to 115-4 and may generate switching control signals S1 to S4for the switches Q1 to Q4. In detail, the current control circuit unit118 generates the switching control signals S1 to S4 so that theconstant current control circuit units 115-1 to 115-4 are sequentiallyoperated depending on the closed state (turned-on state) or the openstate (turned-off state) of the switches Q1 to Q4. That is, the currentcontrol circuit unit 118 receive downstream currents from the constantcurrent control circuit units 115-2 to 115-4 in a subsequent stage, andswitches relevant switches S1 to S4 to an open state (turned-off state)when any one of the received currents reaches a predetermined value. Forexample, for the first switching control signal S1, the current controlcircuit unit 118 receives downstream currents from the constant currentcontrol circuit units 115-2 to 115-4 in a subsequent stage and controlthe first switching control signal S1 to switch the first switch Q1 toan open state when any of the currents reaches a predetermined value.For the second switching control signal S2, the current control circuitunit 118 receives downstream currents from the constant current controlcircuit units 115-3 and 115-4 in a subsequent stage and control thesecond switching control signal S2 to switch the second switch Q2 to anopen state (turned-off state) when any one of the currents reaches thepredetermined value. For the third switch control signal S3, the currentcontrol circuit unit 118 receives downstream current from the constantcurrent control circuit unit 115-4 in a subsequent stage, and controlthe third switching control signal S3 to switch the third switch Q3 toan open state (turned-off state) when the current reaches thepredetermined value.

Further, the current control circuit unit 118 generates PWM signalsrequired to control a mean value of the currents flowing through theswitches Q1 to Q4. The current control circuit unit 118 may detect thecurrents flowing through the constant current control circuit units115-1 to 115-4 regardless of the AC power source, and then control amean value of driving currents flowing through the LED units 113-1 to113-4. For example, when the AC voltage is higher than a referencevoltage level, the driving times of the switches Q1 to Q4 are reduced byreducing the duty cycle of a relevant PWM signal so that the intervals,during which the LED units 113-1 to 113-4 are turned on, are reduced. Incontrast, when the AC voltage is lower than a reference voltage, thedriving times of the switches Q1 to Q4 are increased by increasing theduty cycle of a relevant PWM signal so that the intervals, during whichthe LED units 113-1 to 113-4 are turned on, are increased.

Meanwhile, since the current control circuit unit 118 drives theswitches Q1 to Q4 using the PWM signals, LED driving current in eachstage is generated in the form of a pulse wave. That is, the currentcontrol circuit unit 118 generates signals for controlling Vgs of theswitches Q1 to Q4 so that the driving current of each of the LED units113-1 to 113-4 satisfies preset mean current. In this case, the switchesQ1 to Q4 are operated in a switching (ON/OFF) region, so that thedriving current of each of the LED units 113-1 to 113-4 is formed in theshape of a pulse having a certain duty cycle.

The PWM signal generation unit 30 may include a frequency detection unit31 for detecting the frequency of the AC power source 11, a referencefrequency oscillation circuit 32 for oscillating at a referencefrequency different from the detected frequency, a frequency divisioncircuit 33 for dividing the reference frequency, and a PWM outputdecision unit 34 for deciding on PWM output using frequency-dividedsignals.

The frequency detection unit 31 generates a square wave signal bydetecting zero crossings (zero crossing detection) in the AC powersource 11, and the reference frequency oscillation circuit 32 generatesa reference signal having a PWM frequency synchronized with thegenerated square wave signal. In this case, the frequency of theoscillation signal can be set to various frequencies. The frequencydivision circuit 33 divides the reference PWM frequency signal by amultiple of an integer. The signal which has been frequency-divided inthis way has a duty cycle of 50%, and is frequency-divided by an integern (Fs/n) from a clock pulse, the ratio of ON/OFF times of which is 1.Here, the frequency-divided signal is the reference signal of the PWMoutput decision unit 34, and the PWM output decision unit 34 generates nPWM decision signals PWM1 to PWMn corresponding to the number ofchannels, which will be described in detail with reference to FIG. 18.

FIG. 18 is a waveform diagram showing PWM decision signals obtained byfrequency division in the LED luminescence apparatus according to theexemplary embodiment of the present invention.

As shown in FIG. 18, the PWM output decision unit 34 outputs n PWMdecision signals PWM1 to PWMn using a reference PWM frequency signal Fsand a 2-frequency-divided signal Fs/2. That is, the PWM output decisionunit 34 combines n channels using a logical expression of the referencesignal Fs and the frequency-divided signal Fs/2, and then generates PWMdecision signals. For example, when four PWM decision signals PWM1 toPWM4 are generated, the first PWM decision signal PWM1 can be generatedby performing a logical OR operation on the inverted reference signal Fsand the 2-frequency-divided signal Fs/2, the second PWM decision signalPWM2 can be generated by performing a logical OR operation on aninverted reference signal Fs and an inverted 2-frequency-divided signalFs/2, the third PWM decision signal PWM3 is the reference signal Fs, andthe fourth PWM decision signal PWM4 can be generated by performing alogical NOT operation on the reference signal Fs. Therefore, the PWMdecision signals PWM1 to PWM4 have the form of pulses that repeatedlyoverlap one another. That is, in FIG. 18, in a single cycle of the2-frequency-divided signal Fs/2, in a first interval, the first PWMdecision signal PWM1 and the third PWM decision signal PWM3 overlap eachother, in a second interval, the first PWM decision signal PWM1, thesecond PWM decision signal PWM2 and the fourth PWM decision signal PWM4overlap one another, in a third interval, the second PWM decision signalPWM2 and the third PWM decision signal PWM3 overlap each other, and afourth interval, the first PWM decision signal PWM1, the second PWMdecision signal PWM2 and the fourth PWM decision signal PWM4 overlap oneanother.

The operation of the LED luminescence apparatus using AC power accordingto the present exemplary embodiment shown in FIG. 15 will be describedin detail below.

The operation of the LED luminescence apparatus using AC power shown inFIG. 16 and FIG. 17 according to the present exemplary embodiment willnow be described in detail.

First, when AC voltage is input by the AC power source 11 to therectification circuit unit 12, the rectification circuit unit 12rectifies the AC voltage and outputs unidirectional ripple voltage Vrec.As shown in FIG. 15, the output voltage of the AC power source 11, thatis, voltage input to the rectification circuit unit 12, is AC voltagehaving both a positive direction and a negative direction, and thevoltage output from the rectification circuit unit 12 has the form ofunidirectional ripple voltage Vrec in which voltage in the negativedirection is converted into voltage in the positive direction. Such aripple voltage Vrec is supplied to the plurality of LED channel units100 to n×100. Hereinafter, a description will be made on the basis ofthe LED channel unit 1 100 because the operations of the LED channelunits 100 to n×100 are identical to each other.

As the ripple voltage Vrec input to the LED channel unit 1 100increases, the LED units 113-1 to 113-4 may sequentially emit light. Thelight emission operations of the LED units are described with referenceto FIG. 4 and FIG. 5.

FIG. 4 is a waveform diagram showing the waveforms of AC voltage and ACcurrent supplied to LEDs in the LED luminescence apparatus according tothe present exemplary embodiment.

FIG. 5 is a waveform diagram showing the waveforms of the controlsignals of the switches provided in the LED luminescence apparatusaccording to the present exemplary embodiment, the waveform of currentflowing through the switches, and the waveform of current supplied tothe LEDs over time.

Further, FIG. 4 and FIG. 5 illustrate only a single cycle of ripplevoltage Vrec supplied by the rectification circuit unit 12. The reasonfor this is that the same operation is performed in the remaining cyclesof the ripple voltage Vrec.

When the magnitude of the ripple voltage Vrec supplied to the LED units113-1 to 113-4 increases, and the ripple voltage Vrec reaches thedriving voltage (forward voltage: Vf1) of the first LED unit 113-1,current flows through the first LED unit 113-1 and then light is emitted(at time t0 of FIG. 4 and FIG. 5). In this case, the first switch Q1 tothe fourth switch Q4 are initially set to a closed state (turned-onstate). Current corresponding to such input voltage Vf1 flows through apath to the first constant current control circuit unit 115-1 via thefirst LED unit 113-1. In this case, the first switch Q1 controls currentpassing through the first constant current control circuit unit 115-1 toa constant value in response to a control signal from the first constantcurrent control circuit unit 115-1. The first constant current controlcircuit unit 115-1 performs constant current control so that currentpreset to drive the first LED unit 113-1 can flow therethrough. Theoperation in which the first LED unit 113-1 initiates light emissioncorresponds to a time interval t0-t1. Here, the current control circuitunit 118 detects the current of the first constant current controlcircuit unit 115-1, generates a PWM signal depending on an error betweenthe detected current and the reference current, and then drives thefirst switch Q1.

In this case, in response to the PWM decision signals PWM1 to PWMngenerated by the PWM output decision unit 34, the individual LED channelunits 100 to 400 can be sequentially operated. That is, as shown in FIG.5, the LED channel units 100 to 400 are sequentially driven in responseto the PWM decision signals PWM1 to PWM4, so that the first LED units113-1 of the individual LED channel units 100 to 400 are sequentiallyturned on. Here, since the PWM decision signals PWM1 to PWM4 overlap oneanother in some intervals, two or three of the LED channel units 100 to400 are simultaneously driven in some intervals, in which case the firstLED units 113-1 of the LED channel units 100 to 400 are simultaneouslyturned on and, consequently, the LED driving current is generated in theform of DC level-shifted current.

Next, when the magnitude of the ripple voltage Vrec further increasesand voltage applied to the second LED unit 113-2 becomes the drivingvoltage of the second LED unit 113-2 (when the magnitude of the ripplevoltage Vrec becomes Vf2), current flows through the second LED unit113-2, and then light is emitted (at time t1 of FIG. 4 and FIG. 5).Here, current corresponding to the input voltage Vf2 also flows througha path to the second constant current control circuit unit 115-2 via thesecond LED unit 113-2. In this case, the current control circuit unit118 detects that the current of the second constant current controlcircuit unit 115-2 is a predetermined value, generates the firstswitching control signal S1, and then opens (turns off) the first switchQ1. At the same time, the second switch Q2 performs control such that,in response to the control signal from the second constant currentcontrol circuit unit 115-2, current passing and flowing through thesecond constant current control circuit unit 115-2 becomes currentpreset to drive the first LED unit 113-1 and the second LED unit 113-2.

Using this operation, control may be performed such that constantcurrent flows through the first LED unit 113-1 and the second LED unit113-2. Further, as shown in FIG. 4 and FIG. 5, at time t1, the firstswitch Q1 is turned off, and stepped input current can be formed usingconstant current control performed by the second constant currentcontrol circuit unit 115-1. Here, the current control circuit unit 118detects the current of the second constant current control circuit unit115-2, generates a PWM signal depending on an error between the detectedcurrent and the reference current, and then drives the second switch Q2.Therefore, as shown in FIG. 5, during the time interval t1-t2, the LEDchannel units 100 to 400 are sequentially driven in response to the PWMdecision signals PWM1 to PWM4, so that the first LED unit 113-1 and thesecond LED unit 113-2 of the LED channel units 100 to 400 are turned on.Here, since the PWM decision signals PWM1 to PWM4 overlap one another insome intervals, two or three of the LED channel units 100 to 400 aresimultaneously driven in some intervals, in which case the first andsecond LED units 113-1 and 113-2 of the LED channel units 100 to 400 aresimultaneously turned on and, consequently, the LED driving current isgenerated in the form of DC level-shifted current.

Similarly to the above description, when the ripple voltage Vrec furtherincreases and voltage applied to the third LED unit 113-3 becomes thedriving voltage of the third LED unit 113-3 (when the magnitude of theripple voltage Vrec becomes Vf3), current flows through the third LEDunit 113-3, and light is emitted (at time t2 of FIG. 4 and FIG. 5). Inthis case, current corresponding to the input voltage Vf3 also flowsthrough a path to the third constant current control circuit unit 115-3via the third LED unit 113-3. Here, the current control circuit unit 118detects that the current of the third constant current control circuitunit 115-3 is a predetermined value, generates second switching controlsignal S2, and then opens (turns off) the second switch Q2. The firstswitching control signal S1 is maintained in its previous state, so thatthe first switch Q1 is maintained in an open (turned-off) state. At thesame time, the third switch Q3 performs control such that, in responseto the control signal from the third constant current control circuitunit 115-3, current passing and flowing through the third constantcurrent control circuit unit 115-3 becomes current preset to drive thefirst LED unit 113-1 to the third LED unit 113-3.

Using this operation, control may be performed such that constantcurrent flows through the first LED unit 113-1, the second LED unit113-2, and the third LED unit 113-3. Further, as shown in FIG. 4 andFIG. 5, at time t2, the first switch Q1 and the second switch Q2 areturned off, and stepped input current can be formed using constantcurrent control performed by the third constant current control circuitunit 115-3. Here, the current control circuit unit 118 detects thecurrent of the third constant current control circuit unit 115-3,generates a PWM signal depending on an error between the detectedcurrent and the reference current, and then drives the third switch Q3.Therefore, as shown in FIG. 4, during the time interval t2-t3, the LEDchannel units 100 to 400 are sequentially driven in response to the PWMdecision signals PWM1 to PWM4, so that the first LED unit 113-1 to thethird LED unit 113-3 of the LED channel units 100 to 400 are turned on.Here, since the PWM decision signals PWM1 to PWM4 overlap one another insome intervals, two or three of the LED channel units 100 to 400 aresimultaneously driven in some intervals, in which case the first tothird LED units 113-1 to 113-3 of the LED channel units 100 to 400 aresimultaneously turned on and, consequently, the LED driving current isgenerated in the form of DC level-shifted current.

Similarly to the above description, when the ripple voltage Vrec furtherincreases and voltage applied to the fourth LED unit 113-4 becomes thedriving voltage of the fourth LED unit 113-4 (when the magnitude of theripple voltage Vrec becomes Vf4), current flows through the fourth LEDunit 113-4, and light is emitted (at time t3 of FIG. 4 and FIG. 5). Inthis case, current corresponding to the input voltage Vf4 also flowsthrough a path to the fourth constant current control circuit unit 115-4via the fourth LED unit 113-4. Here, the current control circuit unit118 detects that the current of the fourth constant current controlcircuit unit 115-4 is a predetermined value, generates a third switchingcontrol signal S3, and then opens (turns off) the third switch Q3. Thefirst and second switching control signals S1 and S2 are maintained inits previous state, so that the first and second switches Q1 and Q2 aremaintained in an open (turned-off) state. At the same time, the fourthswitch Q4 performs control such that, in response to the control signalfrom the fourth constant current control circuit unit 115-4, currentpassing and flowing through the fourth constant current control circuitunit 115-4 becomes current preset to drive the first LED unit 113-1 tothe fourth LED unit 113-4.

Using this operation, control may be performed such that constantcurrent flows through the first LED unit 113-1, the second LED unit113-2, the third LED unit 113-3, and the fourth LED unit 113-4. Further,as shown in FIG. 4 and FIG. 5, at time t3, the third switch is turnedoff, and stepped input current can be formed using constant currentcontrol performed by the fourth constant current control circuit unit115-4. Here, the current control circuit unit 118 detects the current ofthe fourth constant current control circuit unit 115-4, generates a PWMsignal depending on an error between the detected current and thereference current, and then drives the fourth switch Q4. Therefore, asshown in FIG. 5, during the time interval t3-t4, the LED channel units100 to 400 are sequentially driven in response to the PWM decisionsignals PWM1 to PWM4, so that the first LED unit 113-1 to the fourth LEDunit 113-4 of the LED channel units 100 to 400 are turned on. Here,since the PWM decision signals PWM1 to PWM4 overlap one another in someintervals, two or three of the LED channel units 100 to 400 aresimultaneously driven in some intervals, in which case the first tofourth LED units 113-1 to 113-4 of the LED channel units 100 to 400 aresimultaneously turned on and, consequently, the LED driving current isgenerated in the form of DC level-shifted current.

When the ripple voltage Vrec passes over a peak and gradually decreases,the LED units are sequentially turned off in the sequence from thefourth LED unit 113-4 to the first LED unit 113-1. When the fourth LEDunit 113-4 is turned off (at time t4), the current control circuit unit118 detects that the current of the fourth constant current controlcircuit unit 115-4 is not the predetermined value, inverts the thirdswitching control signal S3, and then closes (turns on) the third switchQ3. In this case, the first switching control signal S1 and the secondswitching control signal S2 are maintained in their previous states, sothat the first switch Q1 and the second switch Q2 are maintained in anopen (turned-off) state. At the same time, current flows into the thirdconstant current control circuit unit 115-3, and constant currentcontrol is initiated so that preset current is maintained to drive thefirst to third LED units 113-1 to 113-3.

In this case, the current control circuit unit 118 detects the currentof the third constant current control circuit unit 115-3, generates aPWM signal depending on an error between the detected current and thereference current, and then drives the third switch Q3. Therefore, asshown in FIG. 5, during the time interval t4-t5, the LED channel units100 to 400 are sequentially driven in response to the PWM decisionsignals PWM1 to PWM4, so that the first LED unit 113-1 to the third LEDunit 113-3 of the LED channel units 100 to 400 are turned on. Here,since the PWM decision signals PWM1 to PWM4 overlap one another in someintervals, two or three of the LED channel units 100 to 400 aresimultaneously driven in some intervals, in which case the first tothird LED units 113-1 to 113-3 of the LED channel units 100 to 400 aresimultaneously turned on and, consequently, the LED driving current isgenerated in the form of DC level-shifted current.

A subsequent current control operation is performed in the reverse orderof the constant current control performed during the above-describedinterval t0 to t3, and thus a detailed description thereof is omitted.

Although the present exemplary embodiment has been described such thatLED driving current is increased or decreased in a stepped shape viamulti-stage constant current control, the present invention is notlimited thereto and reference current for constant current control canbe set to various forms so that the waveform of the LED driving currentcan also be changed.

Hereinafter, the peak current control and average current control of theLED driving current will be described in detail with reference to FIG.19 and FIG. 20.

FIG. 19 is a detailed block diagram showing PWM control in the LEDluminescence apparatus according to an exemplary embodiment of thepresent invention.

FIG. 20 is a waveform diagram showing the waveforms of LED drivingcurrents depending on PWM output signals in the LED luminescenceapparatus according to the present exemplary embodiment.

In order to describe an operation in which the LED channel units 100 to400 are sequentially operated in response to PWM decision signals PWM1to PWMn, and then the LED driving currents are generated in the formwhich they overlap each other in some intervals, FIG. 19 illustrates thefirst LED units 113-1 to 413-1 implemented in the first stages of therespective LED channel units 100 to 400 on the basis of PWM decisionsignals PWM1 to PWM4.

As shown in FIG. 19, when the rectified ripple voltage Vrec becomes thedriving voltage Vf1 of the first LED units 113-1 to 413-1, the first LEDunits 113-1 to 413-1 in the respective LED channel units 100 to 400 aredriven.

In this case, the PWM output decision unit 34 generates the PWM decisionsignals PWM1 to PWM4, as shown in FIG. 18, and provides them to thecurrent control circuit units 118 to 418, respectively. The currentcontrol circuit units 118 to 418 of the LED channel units 100 to 400 aresequentially operated in response to the PWM decision signals PWM1 toPWM4.

That is, as shown in FIG. 19, the LED channel unit 1 100 is driven inresponse to the first PWM decision signal PWM1. The current controlcircuit unit 118-1 of the LED channel unit 1 100 outputs the switchcontrol signal S1, so that the first LED unit 113-1 emits light via theconstant current control unit 110-1. That is, LED driving current Ch1 isformed by the LED channel unit 1 100 in response to the first PWMdecision signal PWM1. Here, the LED driving current Ch1 of the LEDchannel unit 1 100 is formed in the same pattern as the first PWMdecision signal PWM1, for example, it does not flow in the thirdinterval during the four intervals constituting a single cycle of the2-frequency-divided signal Fs/2.

Next, the LED channel unit 2 200 is driven in response to the second PWMdecision signal PWM2. The current control circuit unit 218-1 of the LEDchannel unit 2 200 outputs the switch control signal S1, so that thefirst LED unit 213-1 emits light via the constant current control unit210-1. That is, LED driving current Ch2 is formed by the LED channelunit 2 200 in response to the second PWM decision signal PWM2. Here, theLED driving current Ch2 of the LED channel unit 2 200 is formed in thesame pattern as the second PWM decision signal PWM2, for example, itdoes not flow in the first interval during the four intervalsconstituting a single cycle of the 2-frequency-divided signal Fs/2.

Thereafter, the LED channel unit 3 300 is driven in response to thethird PWM decision signal PWM3. The current control circuit unit 318-1of the LED channel unit 3 300 outputs the switch control signal S1, sothat the first LED unit 313-1 emits light via the constant currentcontrol unit 310-1. That is, LED driving current Ch3 is formed by theLED channel unit 3 300 in response to the third PWM decision signalPWM3. Here, the LED driving current Ch3 of the LED channel unit 3 300 isformed in the same pattern as the third PWM decision signal PWM3, forexample, it does not flow in the second and fourth intervals during thefour intervals constituting a single cycle of the 2-frequency-dividedsignal Fs/2.

Finally, the LED channel unit 4 400 is driven in response to the fourthPWM decision signal PWM4. The current control circuit unit 418-1 of theLED channel unit 4 400 outputs the switch control signal S1, so that thefourth LED unit 413-1 emits light via the constant current control unit410-1. That is, LED driving current Ch4 is formed by the LED channelunit 4 400 in response to the fourth PWM decision signal PWM4. Here, theLED driving current Ch4 of the LED channel unit 4 400 is formed in thesame pattern as the fourth PWM decision signal PWM4, for example, itdoes not flow in the first and third intervals during the four intervalsconstituting a single cycle of the 2-frequency-divided signal Fs/2.

Consequently, since the LED channel units 100 to 400 are sequentiallydriven in response to the PWM decision signals PWM1 to PWM4, the totalLED driving current ILED obtained by summing the driving currents of thefirst LED units 113-1 to 413-1 of the LED channel units 100 to 400 canbe generated in the form of DC level-shifted pulse waves that overlapone another in some intervals. That is, in FIG. 20, in a single cycle ofthe 2-frequency-divided signal Fs/2, in a first interval, the drivingcurrent Ch1 of the LED channel unit 1 100 and the driving current Ch3 ofthe LED channel unit 3 300 overlap each other, in a second interval, thedriving current Ch1 of the LED channel unit 1 100, the driving currentCh2 of the LED channel unit 2 200, and the driving current Ch4 of theLED channel unit 4 400 overlap one another, in a third interval, thedriving current Ch2 of the LED channel unit 2 200 and the drivingcurrent Ch3 of the LED channel unit 3 300 overlap each other, and in thefourth interval, the driving current Ch1 of the LED channel unit 1 100,the driving current Ch2 of the LED channel unit 2 200, and the drivingcurrent Ch4 of the LED channel unit 4 400 overlap one another.

FIG. 21 is a block diagram of an LED luminescence apparatus according toan exemplary embodiment of the present invention.

FIG. 22A and FIG. 22B are waveform diagrams illustrating an LED drivingcurrent waveforms without and with an improved LED OFF interval,respectively, in the LED luminescence apparatus according to the presentexemplary embodiment.

Although FIG. 21 illustrates only the LED channel unit 1 100, theindividual LED channel units 100 to 400 have the same configuration sothat they are operated in response to the PWM decision signals PWM1 toPWM4.

Since the LED luminescence apparatus according to the exemplaryembodiment shown in FIG. 21 is the same as that of the exemplaryembodiment described above with respect to FIG. 19 except for a fifthLED unit 113-5, connected in parallel to the LED units 113-1 to 113-4,and a corresponding constant current control unit 110-5, descriptions ofthe same elements will be omitted here.

The fifth LED unit 113-5 is operated at a driving voltage Vf5 that islower than the driving voltage Vf1 of the first LED unit 113-1, and theconstant current control unit 110-5 and the current control circuit unit118 are operated at the corresponding driving voltage. That is, thecurrent control circuit unit 118, such as that shown in FIG. 21, outputsa control signal S5 for operating the fifth LED unit 113-5 to theconstant current control unit 110-5 when the input AC power is lowerthan the driving voltage of the first LED unit 113-1. Furthermore, thecurrent control circuit unit 118 outputs a control signal S5 forpreventing the fifth LED unit 113-5 from operating to the constantcurrent control unit 110-5 when the input AC power is equal to or higherthan the driving voltage of the first LED unit 113-1.

Using this operation, the fifth LED unit 113-5 first emits light atvoltage Vf5 where the input power is lower than the driving voltage ofthe first LED unit 113-1 in multi-stage stepped current operation,thereby reducing the LED OFF interval. That is, as shown in FIG. 22A,without the fifth LED unit 113-5, for example, the LED units 113-1 to113-4 do not emit light in the interval where the input voltage is lessthan the driving voltage Vf1 of the first LED unit 113-1, and thereforeLED OFF interval A occurs in the early interval of stepped drivingcurrent.

However, according to the present exemplary embodiment, in this earlyinterval, the fifth LED unit 113-5 having driving voltage Vf5 lower thanthe driving voltages Vf1 to Vf4 of the LED driving units 113-1 to 113-4emits light, thereby reducing the LED OFF interval A to the LED OFFinterval B achieved by the fifth LED unit 113-5, as shown in FIG. 22B.

As described above, the exemplary embodiments of the present inventionmay have constant current control units configured using a plurality ofchannels and the outputs of the constant current control units arecontinuously provided in response to PWM decision signals obtained byfrequency division and interleaving, so that the cost of the powercircuit of an LED luminescence apparatus can be reduced and the smallsize and light weight of the LED luminescence apparatus can be realizedbecause an EMI filter is configured using only a resistor and acapacitor and therefore simplifying the structure of the LEDluminescence apparatus.

Furthermore, the present invention is additionally provided with an LEDwhose driving voltage Vf is low, thereby reducing light output OFFintervals.

FIG. 23 is a waveform diagram showing PWM decision signals obtained byfrequency division in the LED luminescence apparatus according to anexemplary embodiment of the present invention. The circuit configurationof the exemplary embodiment is the same as in FIG. 17, and detaileddescription thereof will be omitted herein.

As shown in FIG. 23, the PWM output decision unit 34 outputs n PWMdecision signals PWM1 to PWMn using a reference PWM frequency signal Fsand a 2-frequency-divided signal Fs/2. That is, the PWM output decisionunit 34 combines n channels using a logical expression of the referencesignal Fs and the frequency-divided signal, and then generates PWMdecision signals PWM1 to PWMn. For example, when four PWM decisionsignals are generated, the first PWM decision signal PWM1 can begenerated by performing a logical AND operation on the reference signalFs and the 2-frequency-divided signal Fs/2, the second PWM decisionsignal PWM2 can be generated by performing a logical AND operation on aninverted reference signal Fs and the 2-frequency-divided signal Fs/2,the third PWM decision signal PWM3 can be generated by performing alogical AND operation on the reference signal Fs and an inverted2-frequency-divided signal Fs/2, and the fourth PWM decision signal PWM4can be generated by performing a logical AND operation on an invertedreference signal Fs and an inverted 2-frequency-divided signal Fs/2.Therefore, the PWM decision signals PWM1 to PWM4 have the forms ofpulses which are sequentially output without overlapping one another.

The operation of the LED luminescence apparatus using AC power shown inFIG. 16 and FIG. 17 according to the present exemplary embodiment isdescribed above. The light emission operation of the LED units isdescribed above with reference to FIG. 4 and FIG. 5. In response to thePWM decision signals PWM1 to PWMn generated by the PWM output decisionunit 34, the individual LED channel units 100 to 400 can be sequentiallyoperated. That is, as shown in FIG. 5, the LED channel units 100 to 400are sequentially driven in response to the PWM decision signals PWM1 toPWM4, so that the first LED units 113-1 of the LED channel units 100 to400 are turned on, and consequently the LED driving currents are formedin the shape of continuous current.

FIG. 24 is a waveform diagram showing the waveforms of LED drivingcurrents depending on PWM output signals in the LED luminescenceapparatus according to the present exemplary embodiment, which issimilar to the waveform diagram described above with respect to FIG. 20.However, in this case, FIG. 24 shows the waveforms of LED drivingcircuits based on FIG. 23. The PWM output decision unit 34 generates thePWM decision signals PWM1 to PWM4, as shown in FIG. 23, and providesthem to the current control circuit units 118 to 418, respectively. Thecurrent control circuit units 118 to 418 of the LED channel units 100 to400 are sequentially operated in response to the PWM decision signalsPWM1 to PWM4. That is, as shown in FIG. 24, the LED channel units 1through 4 are driven in response to the first PWM decision signal PWM1through the fourth PWM decision signal PWM4, respectively.

Consequently, since the LED channel units 100 to 400 are sequentiallydriven in response to the PWM decision signals PWM1 to PWM4, total LEDdriving current ILED obtained by summing up the driving currents of thefirst LED units 113-1 to 413-1 of the LED channel units 100 to 400 canbe formed as continuous current.

As described above, exemplary embodiments of the present inventiondisclose that constant current control units are configured for aplurality of channels and the outputs of the constant current controlunits are continuously provided in response to PWM decision signalsobtained by frequency division, so that the cost of the power circuit ofan LED luminescence apparatus can be reduced and the small size andlight weight of the LED luminescence apparatus can be realized becausethere is no need to separately provide an EMI filter composed of a coiland a capacitor.

FIG. 25 is a block diagram showing an LED driving circuit implemented asan LED driving circuit package according to an exemplary embodiment ofthe present invention.

As shown in FIG. 25, an LED driving circuit package 1000 according tothe present exemplary embodiment may include a rectification unit 12 forreceiving AC voltage V_(ac) from AC power source 11 and converting theAC voltage V_(ac) into ripple voltage V_(BD), a low voltage controlcircuit unit 1200 for generating various types of low voltage signalsrequired to drive LEDs using the ripple voltage V_(BD) output from therectification unit 12 and outputting the low voltage signals, and an LEDdriving switch unit 1300 for controlling current that is to be suppliedto external LEDs being supplied with the ripple voltage V_(BD).

The rectification unit 12 may include a plurality of diodes D₁ to D₄constituting a bridge circuit, and is configured to convert the ACvoltage V_(ac) into the ripple voltage V_(BD) and output the ripplevoltage V_(BD). The ripple voltage V_(BD) may be supplied to theexternal LEDs via the external connection terminals of the LED drivingcircuit package.

The low voltage control circuit unit 1200 may include a circuit powersupply unit 1210 for generating low voltage power that can be supplied,as supply voltage, to various types of internal circuits using theripple voltage V_(BD) generated by the rectification unit 12, a voltagedetection unit 1220 for detecting the magnitude of the ripple voltageV_(BD), a reference frequency generation unit 1230 for operating usingthe low voltage power generated by the circuit power supply unit 1210and generating a reference frequency, and a reference pulse generationunit 1240 for operating using the low voltage power generated by thecircuit power supply unit 1210 and generating a reference pulse requiredto control the operation of the LED driving switch unit 1300 accordingto the reference frequency generated by the reference frequencygeneration unit 1230 and the magnitude of the voltage detected by thevoltage detection unit 1220.

In order to implement the above-described circuits, the low voltagecontrol circuit unit 1200 has resistive elements required to divide theripple voltage V_(BD) which is a high voltage.

The LED driving switch unit 1300 may include a plurality of switch units1310 to 1340 and a plurality of current control units 1350 to 1380. Theplurality of switch units 1310 to 1340 may be connected to therespective cathodes of a plurality of external series-connected LEDsLED₁ to LED₄ that form a single channel.

The plurality of current control units 1350 to 1380 control currentswhich are supplied to the LEDs via the switch units so as to be constantcurrents.

For example, when the voltage detection unit 1220 detects the ripplevoltage V_(BD) and the ripple voltage reaches a preset threshold, thereference pulse generation unit 1240 generates a reference pulse to turnon the first switch unit 1310 so that the first switch unit 1310 entersa conductive state, and to turn off the remaining second to fourthswitch units 1320 to 1340 so that the switches 1320 to 1340 enter anopen state. Using this operation, current is applied to the first LEDLED₁ and then the first LED LED₁ emits light. In this case, the firstcurrent control unit 1350 controls current flowing through the first LEDLED₁ and the first switch unit 1310 as to be constant current.

Next, when the voltage detection unit 1220 detects the ripple voltageV_(BD) and the ripple voltage reaches another preset threshold, thereference pulse generation unit 1240 generates a second reference pulseto turn on the second switch unit 1320 so that the second switch unit1320 enters a conductive state, and to turn off the remaining first,third and fourth switch units 1310, 1330 and 1340 so that the switches1310, 1330 and 1340 enter an open state. Using this operation, currentis applied to the first and second LEDs LED₁ and LED₂ and then the firstand second LEDs LED₁ and LED₂ emit light. In this case, the secondcurrent control unit 1360 controls current flowing through the first andsecond LEDs LED₁ and LED₂ and the second switch unit 1320 as to beconstant current.

Next, when the voltage detection unit 1220 detects the ripple voltageV_(BD) and the ripple voltage reaches a further preset threshold, thereference pulse generation unit 1240 generates a third reference pulseto turn on the third switch unit 1330 so that the third switch unit 1330enters a conductive state, and to turn off the remaining first, secondand fourth switch units 1310, 1320 and 1340 so that the switches 1310,1320 and 1340 enter an open state. Using this operation, current isapplied to the first to third LEDs LED₁ to LED₃ and then the first tothird LEDs LED₁ to LED₃ emit light. In this case, the third currentcontrol unit 1370 controls current flowing through the first to thirdLEDs LED₁ to LED₃ and the third switch unit 1330 as to be constantcurrent.

Next, when the voltage detection unit 1220 detects the ripple voltageV_(BD) and the ripple voltage reaches yet another preset threshold, thereference pulse generation unit 1240 generates a fourth reference pulseto turn on the fourth switch unit 1340 so that the fourth switch unit1340 enters a conductive state, and to turn off the remaining first tothird switch units 1310 to 1330 so that the switches 1310 to 1330 enteran open state. Using this operation, current is applied to the first tofourth LEDs LED₁ to LED₄ and then the first to fourth LEDs LED₁ to LED₄emit light. In this case, the fourth current control unit 1380 controlscurrent flowing through the first to fourth LEDs LED₁ to LED₄ and thefourth switch unit 1340 as to be constant current.

The ripple voltage detected by the voltage detection unit 1220periodically repeats while increasing and decreasing, so that theabove-described LED control performed by the LED driving switch unit1300 may allow stepped current, in which rising and falling ripplevoltage is periodically repeated, to flow through the LED channel CH1.

FIG. 26 is a plan view showing the LED driving circuit package accordingto an exemplary embodiment of the present invention. FIG. 27 is a sidesectional view showing the LED driving circuit package according to thepresent exemplary embodiment.

Referring to FIG. 26 and FIG. 27, the LED driving circuit package 1000according to the present exemplary embodiment may be implemented as aMulti-Chip Package (MCP) including a silicon substrate 2000 and aPrinted Circuit Board (PCB) 2100.

That is, the LED driving circuit package 1000 according to the presentexemplary embodiment includes the PCB 2100, the silicon substrate 2000bonded to the top surface of the PCB 2100, and the rectification unit 12and passive elements 2900 mounted on the top surface of the PCB 2100.

The low voltage control circuit unit 1200 and LED driving switch units1300 a and 1300 b described in FIG. 25 may be integrated into thesilicon substrate 2000 using a semiconductor manufacturing process. FIG.26 illustrates an exemplary embodiment in which two driving switch units1300 a and 1300 b are depicted to drive two LED channels.

The rectification unit 12 may be implemented using four PN junctiondiodes. Generally, as the PN junction diodes, diodes that are able tosuppress reverse voltage having magnitude that is about 1.5 to 2 timesthat of input AC voltage may be used. Therefore, in order to implementboth the rectification unit and the low voltage circuit unit together onthe silicon substrate, an additional process for isolating high voltagefrom low voltage during the manufacturing of the semiconductor devicemay be required. Thus, the diodes used to constitute the rectificationunit 12 may be implemented in such a way that the diodes areindependently mounted on the PCB 2100 using individual elements or thelike.

Meanwhile, some of the diodes included in the rectification unit 12 canbe implemented as overvoltage and surge voltage suppressor diodes suchas Zener diodes or Transient Voltage Suppression (TVS) diodes, ratherthan PN junction diodes. The present exemplary embodiment hasrectification unit 12 diodes that are not implemented in the siliconsubstrate 2000 and are mounted on the PCB 2100, thus enabling elementsto be easily changed in a packaging process.

Further, the passive resistive elements 2900 may be mounted on the PCB2100 in the form of separate individual elements without beingintegrated into the silicon substrate 2000.

Since the circuit of the present exemplary embodiment is supplied withand operated by various types of AC power ranging from 80 Vrms to 265Vrms, it must acquire power (voltage and current) from AC voltage unliketypical circuits that are supplied with and driven by separate externalpower. Therefore, the circuit power supply unit 1210 of the low voltagecontrol circuit unit 1200 requires passive resistive elements havinghigh power consumption. With just a semiconductor manufacturing processusing a silicon substrate, it may be difficult to implement passiveelements having high power consumption, and thus necessary passiveelements 2900 having high power consumption can be mounted on the PCB2100 so as to divide the AC rectified voltage in the present exemplaryembodiment.

In the exemplary embodiment shown in FIG. 26 and FIG. 27, in a region ofthe PCB 2100 to which the silicon substrate 2000 is bonded, an upperheat dissipation pad 3100 may be formed. Further, on the bottom surfaceof the PCB 2100, corresponding to the region in which the upper heatdissipation pad 3100 is formed, a lower heat dissipation pad 3200 may beformed. In addition, vias 2800 that come into direct contact with theupper and lower heat dissipation pads 3100 and 3200 may be formed in thePCB 2100 in order to easily transfer heat from the upper heatdissipation pad 3100 to the lower heat dissipation pad 3200.

In consideration of insulation from the PCB 2100, the silicon substrate2000 may be bonded to the top of the upper heat dissipation pad 3100using a non-conducting adhesive 2700.

Meanwhile, although not shown in the drawings, in a modification of theembodiment shown in FIG. 26 and FIG. 27, the upper heat dissipation pad3100 of the PCB 2100 may be omitted, and the silicon substrate 2000 maybe directly bonded to a region, in which the vias 2800 are formed, usingthe non-conducting adhesive 2700.

The rectification unit 12 and the silicon substrate 2000 are arrangedadjacent to the center portion of the top surface of the PCB 2100, andelectrode pads L, N, A to F, A′ to F′, and 2400 may be formed on the topsurface of the PCB 2100 along the edges of the PCB 2100. The electrodepads L, N, A to F, A′ to F′, and 2400 may form electrical connections tothe rectification unit 12 and the silicon substrate 2000 through wires2300. The electrode pads L, N, A to F, A′ to F′, and 2400 may beelectrically connected to an external connection electrode 2600 formedon the bottom surface of the PCB 2100 through a conductive via 2500.

When forming electrical connections through the wires 2300, theelectrical connections may be formed so that wires through which highvoltage flows and wires through which low voltage flows are spatiallyisolated so as to remove electrical interference therebetween. For thisoperation, it is preferable that the electrode pads L and N to which ACpower is externally applied, and the electrode pads A and A′ to whichthe ripple voltage V_(BD) formed by the rectification unit 12 isapplied, be arranged adjacent to the rectification unit 12, thus thelength of the wires for electrical connections to be made as short aspossible.

The above-described PCB 2100, silicon substrate 2000, rectification unit12, passive elements 2900, and bonding wires 2300 may form an integratedmold part 3000 using various kinds of molding materials including aresin material or the like, and thus are integrally molded together.

FIG. 28 is a plan view showing an LED driving circuit package accordingto an exemplary embodiment of the present invention, and FIG. 29 is aside sectional view showing the LED driving circuit package of FIG. 28.

The embodiment shown in FIG. 28 and FIG. 29 has a structure including asilicon substrate 2000 into which a low voltage control circuit unit1200 and LED driving switch units 1300 a and 1300 b are integrated usinga semiconductor manufacturing process, and a rectification unit 12mounted on the top surface of the silicon substrate 2000.

In the present exemplary embodiment, high voltage diodes constitutingthe rectification unit 12 may be mounted on the silicon substrate 2000using a conducting or non-conductive adhesive (made of, for example, anepoxy material) 4100. In the silicon substrate 2000, a region requiredto mount the high voltage diodes may be provided in an area spaced apartfrom the area in which the low voltage control circuit unit 1200 and theLED driving switch units 1300 a and 1300 b are integrated.

Furthermore, connection pads 4200 for forming electrical connectionsbetween the electrode pads 4400 and the rectification unit 12 may beformed on the silicon substrate 2000. Wires 4300 may be bonded to theconnection pads 4200 so as to individually form electrical connectionsto the rectification unit 12 and to the electrode pads 4400.

The silicon substrate 2000 may be bonded to the top of a heatdissipation pad 4800 to provide heat dissipation. The silicon substrate2000 and the heat dissipation pad 4800 may be mutually bonded to eachother using a non-conducting adhesive 4700 so as to form an electricinsulator.

The above-described heat dissipation pad 4800, silicon substrate 2000,rectification unit 12 and bonding wires 2300 may form an integrated moldpart 3000 using various kinds of molding materials such as a resinmaterial or the like, and thus are integrally molded together. On thebottom surface of the mold part 3000, electrode pads L, N, A to F, A′ toF′, and 4400 may be formed at locations spaced apart from the heatdissipation pad 4800.

These electrode pads L, N, A to F, A′ to F′, and 44 may form electricalconnections to the silicon substrate 2000 via wire bonding while beingused as external connection electrodes for inputting/outputtingelectrical signals to/from the outside of the package.

Similarly to the exemplary embodiment shown in FIG. 26 and FIG. 27, theelectrode pads L, N, A to F, A′ to F′, and 4400 may be formed such thatelectrode pads for high voltage usage are spaced apart from electrodepads for low voltage usage. That is, the electrode pads L and N to whichAC power is externally applied and the electrode pads A and A′ to whichthe ripple voltage V_(BD) formed by the rectification unit 12 isapplied, may be arranged adjacent to the rectification unit 12, thusenabling the length of the wires for electrical connections to be madeas short as possible.

FIG. 30 and FIG. 31 are plan views showing examples of the arrangementof terminals and the implementation of the rectification unit on the topsurface of the silicon substrate in the LED driving circuit package ofFIG. 28 according to exemplary embodiments of the present invention.

As shown in FIG. 30 a diode mounting pad 5102 to mount diodes includedin the rectification unit 12, and connection pads 4200 to formelectrical connections to electrode pads L, N, A to F, A′ to F′, and4400 formed on the bottom surface of the mold part 3000 may be arrangedon the top surface of the silicon substrate 2000.

As shown in FIG. 31, an exemplary embodiment of the present inventionmay be implemented such that some diodes 1100 a of the rectificationunit 12 are mounted on the diode mounting pad 5102 in the form ofindividual elements using a conductive adhesive 4100, and such that theremaining diodes 1100 b are integrated into the silicon substrate.

Another exemplary embodiment of the present invention may be implementedsuch that all diodes used in the rectification unit 12 are mounted onthe diode mounting pad 5102 in the form of individual elements using theconductive adhesive 4100.

FIG. 32 is a diagram showing the arrangement of electrode pads and theconnection between the electrode pads and LEDs in the LED drivingcircuit package according to an exemplary embodiment of the presentinvention.

In FIG. 32, electrode pads A, B, C, D, and E may be connected to LEDsLED₁ to LED₄ forming one channel CH1, and electrode pads A′, B′, C′, D′,and E′ may be connected to LEDs LED₅ to LED₈ forming another channelCH2. The electrode pads F and F′ may be used to adjust currents flowingthrough respective LED channels. Such current adjustment may beperformed using various types of electric and electronic parts (forexample, a resistor, a capacitor, an inductor or a transistor) that areseparately connected to the outside of the package.

As shown in FIG. 32, electrode pads L and N to which AC power is appliedmay be formed on one side of the driving circuit package, and electrodepads A to F and A′ to F′ connected to the LEDs may be arranged betweenchannels to be symmetrical on the remaining sides other than the sideclosest to the electrode pads L and N to which the power is applied.

FIG. 32 illustrates the connection between the LEDs implemented as twochannels, but the present invention is not limited to this connection.Various numbers of channels may be determined depending on the number ofLEDs desired to be driven and the amount of current desired to besupplied to the LEDs, so that the structure of the arrangement of theelectrode pads can be changed.

FIG. 33 is a diagram showing the arrangement of electrode pads and theconnection between the electrode pads and a heat dissipation pad in theLED driving circuit package according to an exemplary embodiment of thepresent invention.

In FIG. 33, AC voltages functioning as power are alternately applied toelectrode pads L and N as positive (+) and negative (−) voltages.Further, unidirectional ripple voltage V_(BD) is applied by therectification unit 12 to electrode pads A and A′. That is, high voltageis instantaneously applied to the electrode pads L, N, A and A′.

Therefore, as shown in FIG. 33, separation distances x₁ and x₂ forinsulation must be achieved among the electrode pads L, N, A and A′. Forexample, the separation distances x₁ and x₂ may range from a minimum of1 mm to a maximum of 5.2 mm. As described above, since the operatingvoltage may have a value from 80 Vrms to 265 Vrms, the separationdistances x₁ and x₂ may be suitably adjusted within the above-describedrange according to the operating voltage. The distances x₁ and x₂ may beincreased as Vrms increases.

Further, in the exemplary embodiment of FIG. 28 and FIG. 29, the area ofa heat dissipation pad 4800 may be increased so as to obtain a high heatdissipation effect. However, if the area of the heat dissipation pad4800 having conductivity is excessively increased, the separationdistances providing insulation between the electrode pads L, N, A and A′to which high voltage is applied may not be achievable. Therefore, theheat dissipation pad 4800 may be formed so that the separation distancex₃ providing insulation from the electrode pads L, N, A and A′ isachieved. The separation distance x₃ may be formed to be substantiallyidentical to the separation distances x₁ and x₂.

FIG. 34 is a diagram showing an example of a luminescence module towhich the LED driving circuit package according to an exemplaryembodiment of the present invention is applied.

As shown in FIG. 34, when the LED driving circuit package according toan exemplary embodiment of the present invention is applied, the LEDdriving circuit package 1000 and the LEDs of individual channels CH1 andCH2 can be arranged together on one surface of the board 8100 of aluminescence module.

In particular, the LEDs of the channels CH1 and CH2 are arranged in aline for each channel and the LED driving circuit package 1000 isdisposed between the LEDs of the respective channels, so that anarrangement of LEDs providing efficient lighting may be possible.

Meanwhile, a heat dissipation means for efficiently discharging heatradiated from the LED driving circuit package 1000 and the LEDs LED₁ toLED₈ may be provided on the board 8100 of the luminescence module 8000.

FIG. 35 is a diagram showing an example of an LED chip which can beapplied to the LED luminescence apparatus of the present inventiondescribed above with respect to FIG. 3, FIG. 4, FIG. 5, and FIG. 6.

As shown in FIG. 35, an LED chip 5000 which is applied to theabove-described LED luminescence apparatus of the present invention canbe implemented as a multi-cell LED chip including a plurality of LEDcells C1 to C20. Each of the plurality of LED cells C1 to C20 includedin the LED chip 5000 forms an electrical connection to neighboring LEDcells, thus forming a single integrated series-connection structure.

Each of the LED units 13-1 to 13-4 according to the exemplary embodimentdescribed in FIG. 3 may be implemented as a single LED or a plurality ofLEDs that are connected in series or in parallel to each other. In theLED chip of FIG. 35, LED cells forming a single row may be used as asingle LED unit. For example, the LED cells C1 to C5 in a first row 5100may form a first LED unit, the LED cells C6 to C10 in a second row 5200may form a second LED unit, the LED cells C11 to C15 in a third row mayform a third LED unit, and the LED cells C16 to C20 in a fourth row 5400may form a fourth LED unit.

As shown in FIG. 3, the LED units of the LED luminescence apparatusinput and output the driving current, and have nodes which form anelectrical connection to switches. In the LED chip of FIG. 35, terminalunits An, Ca, and T1 to T3 which form electrical wiring to the outsideof the chip on cells C6, C11, and C16 may be formed so as toinput/output the driving current and form electrical connections to theswitches. Each of the terminals units An, Ca, and T1 to T3 may be formedin the shape of a pad which has a predetermined area and to which a wirefor forming an electrical connection to the outside is bonded.

FIG. 36 is a plan view showing an LED package using the multi-cell LEDchip of FIG. 35.

The LED package of FIG. 36 may include a board 6100 having a die attacharea 6200 at the center portion thereof, an LED chip 5000 attached tothe die attach area 6200, and a plurality of electrode pad units P1 toP5 formed around the die attach area 6200 and configured to formelectrical connections to the terminal units An, Ca, and T1 to T3 of theLED chip 5000 via wires w1 to w5.

Although not shown in the drawing, a heat dissipation pad foreffectively dissipating and discharging heat generated by the LED chipmay be formed on the die attach area 6200. Further, on a surfaceopposite the one surface of the board to which the LED chip 5000 isattached and on which the electrode pad units P1 to P5 are formed, aplurality of terminal units corresponding to the electrode pad units P1to P5 in a one-to-one correspondence may be formed so as to formelectrical connections to the electrode pad units P1 to P5. Theseterminal units may be connected to a rectification circuit unit and maybe configured to input/output driving current and set up connections toswitches.

FIG. 37A and FIG. 37B are diagrams showing an exemplary embodiment of anLED package which can be applied to the LED luminescence apparatusdescribed above. FIG. 37A is a diagram showing the surface of the LEDpackage to which LED chips are attached, and FIG. 37B is a diagramshowing the opposite surface thereof.

As shown in FIG. 37A, the LED package according to an exemplaryembodiment of the present invention may include a board 7100 having adie attach area 7200 formed at the center portion thereof, a pluralityof LED chips 7310 to 7340 attached to the die attach area, and aplurality of electrode pad units P1 to P5 formed around the die attacharea.

The LED package shown in FIG. 37A has a structure in which a single LEDchip forms a single LED unit, wherein electrical connections between theLED units may be made by a plurality of electrode pad units P1 to P5.

For example, the p-type electrode 7310 p of the first LED chip 7310 maybe wire-bonded to the first electrode pad unit P1, the n-type electrode7310 n of the first LED chip 7310 and the p-type electrode 7320 p of thesecond LED chip 7320 may be wire-bonded in common to the secondelectrode pad unit P2, the n-type electrode 7320 n of the second LEDchip 7320 and the p-type electrode 7330 p of the third LED chip 7330 maybe wire-bonded in common to the third electrode pad unit P3, the n-typeelectrode 7330 n of the third LED chip 7330 and the p-type electrode7340 p of the fourth LED chip 7340 may be wire-bonded in common to thefourth electrode pad unit P4, and the n-type electrode 7340 n of thefourth LED chip 7340 may be wire-bonded to the fifth electrode pad unitP5.

Using this connection structure, the four LED chips form a connectionstructure in which they are connected in series to each other. Further,the first electrode pad unit P1 and the fifth electrode pad unit P5 areconnected to a rectification circuit unit, and the second to fourthelectrode pad units P2 to P4 are respectively connected to a pluralityof switches, thus enabling the LED units to be sequentially driven, asdescribed above.

As shown in FIG. 37A, the p-type electrode 7310 p, 7320 p, 7330 p or7340 p and the n-type electrode 7310 n, 7320 n, 7330 n, or 7340 n areformed at corners located diagonally across from each other on the topsurface of each of the LED chips 7310 to 7340. Further, the LED chips7310 to 7340 may be arranged in a 2×2 matrix form and may be arrangedsuch that one electrode of each LED chip is adjacent to the electrode ofa single neighboring LED chip. By means of this arrangement, wirebonding between the electrode pads formed around the die attach area7200 and the electrodes of the respective LED chips may be implementedso that the wires that are bonded do not intersect or interfere witheach other.

Meanwhile, as shown in FIG. 37B, on a surface opposite the one surfaceof the board shown in FIG. 37A, a plurality of terminal units T1 to T5corresponding to the electrode pad units P1 to P5 in a one-to-onecorrespondence may be formed so as to form electrical connections to theelectrode pad units P1 to P5. The terminal units T1 to T5 makeelectrical contact with circuit patterns or the like on other externalboards, thus forming electrical connections between the LED chips, therectification circuit unit and the switches, as described above.Further, on a corresponding portion of the surface that is below theportion to which the LED chips 7310 to 7340 are attached, there may beformed a heat dissipation pad 7500 for effectively dissipating anddischarging heat radiated from the LED chips 7310 to 7340.

FIG. 38A and FIG. 38B are diagrams showing an exemplary embodiment of anLED package which can be applied to the LED luminescence apparatusdescribed above. FIG. 38A is a diagram showing the surface of the LEDpackage to which the LED chips are attached, and FIG. 38B is a diagramshowing the opposite surface thereof.

Similarly to the above-described LED package of FIG. 37A and FIG. 37B,the LED package according to the present exemplary embodiment mayinclude a board 81 having a die attach area 8200 formed at the centerportion thereof, a plurality of LED chips 8310 to 8340 attached to thedie attach area, and a plurality of electrode pad units P1 to P6 formedaround the die attach area.

The LED package of FIG. 38A has a structure in which the LED chip 8310and the LED chip 8320 form a series-connection via the electrode padunit P2, and the LED chip 8330 and the LED chip 8340 form aseries-connection via the electrode pad unit P5.

In the connection structure of the LED chips, as shown in FIG. 38A, whenan electrical connection is formed between the electrode pad unit P3 andthe electrode pad unit P4, the four LED chips 8310 to 8340 may beconnected in series to one another. In this case, the first electrodepad unit P1 and the sixth electrode pad unit are connected to arectification circuit unit, and the electrode pad unit P2, the electrodepad unit P3 or P4, and the electrode pad unit P5 are individuallyconnected to a plurality of switches, thus enabling the LED units to besequentially driven, as described above.

Meanwhile, in the LED package of FIG. 38A, when the electrode pad unitP1 and the electrode pad unit P4 are electrically connected to eachother, and the electrode pad unit P3 and the electrode pad unit P6 areelectrically connected to each other, an electrical connection structureis formed in which the two series-connected LED chips 8310 and 8320 andthe two series-connected LED chips 8330 and 8340 are connected inparallel to each other. In this case, the electrode pad unit P1 or P4and the electrode pad unit P3 or P4 are connected to the rectificationcircuit unit, and the electrode pad unit P2 and the electrode pad unitP5 may be connected to the switches. In this way, the two LED chips 8310and 8320 can be sequentially driven, and the two LED chips 8330 and 8340can be sequentially driven. In this electrical connection structure,half of the driving voltage and double driving current are requiredcompared to the connection structure of the LED chips shown in FIG. 37Aand FIG. 37B.

As shown in FIG. 38A, the electrical connections between the LED chipsand the electrode pad units have been changed, and thus suitableelectrical connection structures can be formed as occasion demands.

Meanwhile, similarly to the embodiment of FIG. 37A, electrodes havingtwo polarities may be individually formed at corners located diagonallyacross from each other on the top surface of each of the LED chips 8310to 8340 shown in FIG. 38A, and the LED chips 8310 to 8340 may bearranged in a 2×2 matrix form. One electrode of each of the LED chipsmay be arranged adjacent to the electrode of a single neighboring LEDchip.

Further, as shown in FIG. 38B, on a surface opposite the one surface ofthe board shown in FIG. 38A, a plurality of terminal units T1 to T6corresponding to the electrode pad units P1 to P6 in a one-to-onecorrespondence may be formed so as to form electrical connections to theelectrode pad units P1 to P6. The terminal units T1 to T6 makeelectrical contact with circuit patterns or the like on other externalboards, thus forming electrical connections between the LED chips, therectification circuit unit and the switches, as described above.Further, on a corresponding portion of the surface that is below theportion to which the LED chips 8310 to 8340 are attached, there may beformed a heat dissipation pad 8500 for effectively dissipating anddischarging heat radiated from the LED chips 8310 to 8340.

The exemplary embodiments described above with respect to FIG. 3, FIG.4, and FIG. 5, FIG. 6, FIG. 7, FIG. 8, FIG. 9, and FIG. 10 have beendescribed such that the LED driving current increases or decreases in astepped form using multi-stage constant current control. However, thewaveform of the LED driving current may be modified by variously settingreference current for constant current control.

As described above, the series-connected LEDs are sequentially driven atconstant current using AC voltage, so that current that increases ordecreases in a stepped form can be provided as illustrated in FIG. 4 andFIG. 5, and therefore LED driving current approximate to a sinusoidalwave equal to AC voltage is provided, thereby enabling problems relatedto the power factor, THD, etc. to be solved.

Furthermore, current at each stage is controlled to have constantmagnitude, so that constant driving current can be provided even in theevent of variation in AC voltage (distortion, or increase or decrease inthe magnitude of voltage). Thus, the light output efficiency ofAC-driven LEDs can be improved.

FIG. 39 is a waveform diagram illustrating an OFF interval of AC currentprovided to LEDs, in the LED luminescence apparatus using AC poweraccording to an exemplary embodiment of the present invention.

FIG. 39 illustrates two cycles for waveforms of input voltage and inputcurrent of the LED luminescence apparatus using AC power described abovewith respect to FIG. 3, FIG. 4, and FIG. 5.

Referring to FIG. 4 and FIG. 39, the LED luminescence apparatus using ACpower has “LED OFF intervals” where current is not applied to theplurality of LED units 13-1 to 13-N, and thus LEDs do not emit light.The non-light-emitting areas of the LED units 13-1 to 13-4 are aninterval prior to t0 of a first cycle, and an interval from t7 of thefirst cycle to t0 of a second cycle. The non-light-emitting areas aregenerated at points where the ripple voltage becomes the smallest.

Accordingly, an exemplary embodiment of the present invention providesan LED luminescence apparatus using AC power, in which the plurality ofLED units can emit light during entire intervals without generating theabove-described non-light-emitting areas.

FIG. 40 is a block diagram of an LED luminescence apparatus using ACpower according to an exemplary embodiment of the present invention.

Referring to FIG. 40, the LED luminescence apparatus using AC poweraccording to the present exemplary embodiment may include an AC powersource 11, a rectification circuit unit 12, a plurality of LED units13-1 to 13-N, a plurality of switches 14-1 to 14-N, a plurality ofconstant current control circuit units 15-1 to 15-N, a currentcomparison unit 16, and a light output compensation unit 20.

The configuration of the LED luminescence apparatus using AC poweraccording to the present exemplary embodiment is substantially the sameas the configuration of the LED luminescence apparatus using AC poweraccording to the exemplary embodiment described above with respect toFIG. 3, except that the LED luminescence apparatus using AC poweraccording to the present exemplary embodiment further includes the lightoutput compensation unit 20.

Accordingly, for simplification of description, detailed descriptions ofthe AC power source 11, the rectification circuit unit 12, the pluralityof LED units 13-1 to 13-N, the plurality of switches 14-1 to 14-N, andthe plurality of constant current control circuit units 15-1 to 15-N ofthe LED luminescence apparatus using AC power according to the presentexemplary embodiment will be omitted here.

However, the current comparison unit 16 according to the presentexemplary embodiment further outputs the control signal SC, compared tothe exemplary embodiment described above with respect to FIG. 3.

The current comparison unit 16 may receive currents i1 to iN flowingthrough the plurality of switches 14-1 to 14-N from the constant currentcontrol circuit units 15-1 to 15-N, and generate a switching controlsignal SC to control turn-on/turn-off of the switch 22 of the lightoutput compensation unit 20.

That is, the current comparison unit 16 receives the currents i1 to iNsuch that when any one of the currents reaches a preset value, thecurrent comparison unit 16 outputs a control signal to switch the switch22 to be in the open (turn-off) or close (turn-on) state.

For example, the current comparison unit 16 receives the currents i1 toiN from the constant current control circuit units 15-1 to 15-N suchthat when the current i1 reaches a minimum point, the current comparisonunit 16 outputs the control signal SC to switch the switch 22 to be inthe open (turn-off) state, and when the current iN reaches a maximumpoint, the current comparison unit 16 outputs the control signal SC toswitch the switch 22 to be in the close (turn-on) state.

Referring to FIG. 40, the light output compensation unit 20 includes acurrent restriction unit 21, a switch 22, a switch control unit 23, acapacitor C, a first diode D1, and a second diode D2.

One end of the current restriction unit 21 is connected to an output endof the rectification circuit unit 12. The other end of the currentrestriction unit 21 is connected to an anode of the first diode D1. Thecurrent restriction unit 21 is a circuit, which controls the magnitudeof current provided to the capacitor C through the first diode D1 andcurrent filled in the capacitor C, and may be configured by at least oneresistance device.

A cathode of the first diode D1 is connected to one end of the capacitorC. The other end of the capacitor C is connected to the switch 22.

FIG. 40 illustrates one capacitor C, but the capacitor C may beimplemented by a plurality of capacitors, which are connected in seriesor parallel to one another.

The switch 22 of the present disclosure may be configured by using afield effect transistor (FET) device, in which a reverse-direction diodeis provided. The other end of the capacitor C may be connected to adrain terminal of the switch 22. A ground electrode may be connected toa source terminal of the switch 22. The switch control unit 23 may beconnected to a gate terminal of the switch 22.

The switch control unit 23 receives the control signal SC input from thecurrent comparison unit 16, and outputs a control signal, which controlsthe open (turn-off)/close (turn-on) state of the switch 22 depending onthe control signal SC, to the gate terminal of the switch 22.

The anode of the second diode D2 is connected to a node of the firstdiode D1 and the capacitor C. The cathode of the second diode D2 isconnected to a node of the first LED unit 13-1 and the currentrestriction unit 21.

In the present exemplary embodiment, the first diode D1 and the seconddiode D2 may be used for LEDs. If LEDs are implemented by the firstdiode D1 and the second diode D2, the light emission efficiency of theLED luminescence apparatus may increase.

The operation of the light output compensation unit 20 and the lightemitting operation of the plurality of LED units 13-1 to 13-N, which arerelated to each other as described above, will be described withreference to FIG. 41 and FIG. 42.

FIG. 41 is a waveform diagram illustrating waveforms of AC voltage andAC current, which are provided to LEDs, in the LED luminescenceapparatus using AC power according to the present exemplary embodiment.

FIG. 42 is a waveform diagram illustrating waveforms of the controlsignals of the switches provided in the LED luminescence apparatus usingAC power according to the present exemplary embodiment, a waveform ofcurrent flowing through the switches, and a waveform of current providedto LEDs over time.

FIG. 41 and FIG. 42 illustrate the case where the number of LED units is4, that is, N=4. Accordingly, an example of the case where in FIG. 40the value of N is set to 4 will be described.

FIG. 41 and FIG. 42 illustrate two cycles of the ripple voltage providedby the rectification circuit unit 12. The same operation may beperformed in the remaining cycles of the ripple voltage, thus only twocycles are shown for the sake of brevity.

When the magnitude of the ripple voltage provided to the plurality ofLED units 13-1 to 13-4 increases and becomes the driving voltage(forward voltage) Vf1 of the first LED unit 13-1, current flows throughthe first LED unit 13-1 so that the first LED unit 13-1 emits light(time t0 of FIGS. 4 and 5). Here, the first to fourth switches 14-1 to14-4 are initially set to the close state (turn-on state). The inputvoltage Vf1 is a threshold voltage, which enables the first LED unit13-1 to be turned on, and the current corresponding to the input voltageVf1 flows through a path to the first constant current control circuitunit 15-1 via the first LED unit 13-1. In this case, the first switch14-1 maintains its turn-on state and uniformly controls current passingthrough the first constant current control circuit unit 15-1 in responseto a control signal from the first constant current control circuit unit15-1. The first constant current control circuit unit 15-1 performsconstant current control such that reference current preset to drive thefirst LED unit 13-1 can flow. The operation, in which the first LED unit13-1 initiates light emission, corresponds to the time intervals t0 andt1 in FIG. 41 and FIG. 42.

Subsequently, when the magnitude of the ripple voltage furtherincreases, and the voltage applied to the plurality of LED units 13-1 to13-N becomes the driving voltage of the first and second LED units 13-1and 13-2 (when the magnitude of the ripple voltage becomes Vf2), currentflows through the second LED unit 13-2 so that the second LED unit 13-2emits light (time t1 of FIG. 4 and FIG. 5). Here, the input voltage Vf2is a threshold voltage, which enables the first and second LED units13-1 and 13-2 to be turned on, and the current corresponding to theinput voltage Vf2 flows through a path to the second constant currentcontrol circuit unit 15-2 via the second LED unit 13-2. In this case,the current comparison unit 16 senses that the current i2 of the secondconstant current control circuit unit 15-2 is a preset value, andgenerates the first switching control signal S1 to open (turn off) thefirst switch 14-1. At the same time, the second switch 14-2 maintainsits turn-on state and performs control in response to a control signalfrom the second constant current control circuit unit 15-2 such thatcurrent flowing through the second constant current control circuit unit15-2 becomes the same as reference current preset to drive both thefirst and second LED units 13-1 and 13-2.

Using this operation, control may be performed such that constantcurrent flows through the first LED unit 13-1 and the second LED unit13-2. As illustrated in FIG. 41 and FIG. 42, at the time t1, the firstswitch 14-1 is turned off, and stepped input current can be formed bythe constant current control of the second constant current controlcircuit unit 15-2.

Similarly to the above-described procedure, when the ripple voltagefurther increases, and voltage applied to the plurality of LED units13-1 to 13-N becomes the driving voltage of the first to third LED units13-1 to 13-3 (when the magnitude of the ripple voltage becomes Vf3),current flows through the third LED unit 13-3 so that the third LED unit13-3 emits light (time t2 of FIG. 41 and FIG. 42). Here, the inputvoltage Vf3 is a threshold voltage, which enables the first to third LEDunits 13-1 to 13-3 to be turned on, and the current corresponding to theinput voltage Vf3 flows through a path to the third constant currentcontrol circuit unit 15-3 via the third LED unit 13-3. In this case, thecurrent comparison unit 16 senses that the current i3 of the thirdconstant current control circuit unit 15-3 is a preset value, andgenerates the second switching control signal S2 to open (turn off) thesecond switch 14-2. At the same time, the third switch 14-3 maintainsits turn-on state and performs control in response to a control signalfrom the third constant current control circuit unit 15-3 such thatcurrent flowing through the third constant current control circuit unit15-3 becomes the same as reference current preset to drive the first tothird LED units 13-1 to 13-3.

Using this operation, control may be performed such that constantcurrent flows through the first to third LED units 13-1 to 13-3. Asillustrated in FIG. 41 and FIG. 42, at the time t2, the second switch14-2 is turned off, and stepped input current can be formed by theconstant current control of the third constant current control circuitunit 15-3.

Similarly to the above-described procedure, when the ripple voltagefurther increases, and voltage applied to the plurality of LED units13-1 to 13-N becomes the driving voltage of the first to fourth LEDunits 13-1 to 13-4 (when the magnitude of the ripple voltage becomesVf4), current flows through the fourth LED unit 13-4 so that the fourthLED unit 13-4 emits light (time t3 of FIG. 41 and FIG. 42). Here, theinput voltage Vf4 is a threshold voltage, which enables all the first tofourth LED units 13-1 to 13-4 to be turned on, and the currentcorresponding to the input voltage Vf4 flows through a path to thefourth constant current control circuit unit 15-4 via the fourth LEDunit 13-4. In this case, the current comparison unit 16 senses that thecurrent i4 of the fourth constant current control circuit unit 15-4 is apreset value, and generates the third switching control signal S3 toopen (turn off) the third switch 14-3. At the same time, the fourthswitch 14-4 maintains its turn-on state and performs control in responseto a control signal from the fourth constant current control circuitunit 15-4 such that current flowing through the fourth constant currentcontrol circuit unit 15-4 becomes the same as reference current presetto drive the first to fourth LED units 13-1 to 13-4.

Using this operation, control may be performed such that constantcurrent flows through the first to fourth LED units 13-1 to 13-4. Asillustrated in FIG. 41 and FIG. 42, at the time t3, the third switch14-3 is turned off, and stepped input current can be formed by theconstant current control of the fourth constant current control circuitunit 15-4.

Furthermore, in the present exemplary embodiment, when the current i4 ofthe fourth constant current control circuit unit 15-4 reaches a firstpreset value, the current comparison unit 16 generates the controlsignal SC to close (turn on) the switch 22 of the light outputcompensation unit 20.

When the control signal SC is input, the switch control unit 23 closes(turns-on) the switch 22. Then, current flows through the rectificationcircuit unit 12, the current restriction unit 21, the first diode D1,the capacitor C, and the switch 22, and the capacitor C is filled withthe ripple voltage rectified in the rectification circuit unit 12.

A signal output from the switch control unit 23 to the gate terminal ofthe switch 22 is a pulse width modulation (PWM) signal. The capacitor Cis filled with voltage during the time when the switch 22 is turned on.Subsequently, when the ripple voltage passes over a peak and graduallydecreases, and the current i4 of the fourth constant current controlcircuit unit 15-4 reaches a second preset value, a control signal SC toopen (turn off) the switch 22 of the light output compensation unit 20is generated.

When the control signal SC to open (turn off) the switch 22 is input,the switch control unit 23 opens (turns off) the switch 22. Then, thecurrent path formed from the rectification circuit unit 12 to thecapacitor C disappears so that the operation of filling the capacitor Cwith ripple voltage is stopped.

FIG. 41 and FIG. 42 illustrate that the current comparison unit 16outputs the control signal SC to close (turn on) the switch 22 at thetime t3, and the control signal SC to open (turn off) the switch 22 atthe time t4. However, the time to turn on or turn off the switch 22 maybe modified.

However, in order to avoid deteriorating the quality characteristics ofthe input power, in the present exemplary embodiment the capacitor C maybe filled with current during the time when the most current flowsthrough the plurality of LED units 13-1 to 13-N.

When the ripple voltage passes over a peak and gradually decreases, theLED units are sequentially turned off in the sequence from the fourthLED unit 13-4 to the first LED unit 13-1.

When the magnitude of the ripple voltage provided to the plurality ofLED units 13-1 to 13-4 decreases and becomes the driving voltage Vf3 ofthe first to third LED units 13-1 to 13-3, the fourth LED unit 13-4 isturned off (time t4). In this case, the current comparison unit 16senses that the current i4 of the fourth constant current controlcircuit unit 15-4 is not a preset value, and outputs the third switchingcontrol signal S3 to close (turn on) the third switch 14-3, so that thethird switch 14-3 is turned on. The current comparison unit 16 outputsthe first and second switching control signals S1 and S2 to maintainprevious states, so that the first and second switches 14-1 and 14-2maintain their open (turn-off) states. At the same time, the thirdswitch 14-3 maintains its turn-on state, and the third constant currentcontrol circuit unit 15-3 initiates constant current control in responseto a control signal from the third constant current control circuit unit15-3 such that the reference current preset to drive the first to thirdLED units 13-1 to 13-3 is maintained. The light emitting operations ofthe first to third LED units 13-1 to 13-3 correspond to the timeintervals t4 and t5 in FIG. 41 and FIG. 42.

When the magnitude of the ripple voltage further decreases and becomesthe driving voltage Vf2 of the first and second LED units 13-1 and 13-2,the third LED unit 13-3 is turned off (time t5). In this case, thecurrent comparison unit 16 senses that the current i3 of the thirdconstant current control circuit unit 15-3 is not a preset value, andoutputs the second switching control signal S2 to close (turn on) thesecond switch 14-2, so that the second switch 14-2 is turned on. Thecurrent comparison unit 16 outputs the first switching control signal S1to maintain a previous state, so that the first switch 14-1 maintainsits open (turn-off) state. At the same time, the second switch 14-2maintains its turn-on state, and the second constant current controlcircuit unit 15-2 initiates constant current control in response to acontrol signal from the second constant current control circuit unit15-2 such that the reference current preset to drive the first andsecond LED units 13-1 and 13-2 is maintained. The light emittingoperations of the first and second LED units 13-1 and 13-2 correspond tothe time intervals t5 and t6 in FIG. 41 and FIG. 42.

Similarly to the above-described procedure, when the magnitude of theripple voltage further decreases and becomes the driving voltage Vf1 ofthe first LED unit 13-1, the second LED unit 13-2 is turned off (timet6). In this case, the current comparison unit 16 senses that thecurrent i2 of the second constant current control circuit unit 15-2 isnot a preset value, and outputs the first switching control signal S1 toclose (turn on) the first switch 14-1, so that the first switch 14-1 isturned on. The current comparison unit 16 outputs the second to fourthswitching control signals S2 to S4 to maintain previous states, so thatthe second to fourth switches 14-2 to 14-4 maintain their open(turn-off) states. At the same time, the first switch 14-1 maintains itsturn-on state, and the first constant current control circuit unit 15-1initiates constant current control in response to a control signal fromthe first constant current control circuit unit 15-1 such that thereference current preset to drive the first LED unit 13-1 is maintained.The light emitting operation of the first LED unit 13-1 corresponds tothe time intervals t6 and t7 in FIG. 41 and FIG. 42.

When the ripple voltage further decreases, and voltage applied to theplurality of LED units 13-1 to 13-N becomes threshold voltage Vd of thesecond diode D2, current paths to the capacitor C, the second diode D2,and the first LED unit 13-1 are formed. Then, the first LED unit 13-1emits light by current provided from the capacitor C. The light emittingoperation of the first LED unit 13-1 corresponds to the time intervalst7 and t8 in FIG. 41 and FIG. 42.

In the present exemplary embodiment, the threshold voltage Vd of thesecond diode D2 is set to below the first driving voltage Vf1, but maybe modified. For example, if the threshold voltage Vd of the seconddiode D2 is set to the second driving voltage Vf2, the light emittingoperations of the first and second LED units 13-1 and 13-2 maycorrespond to the time intervals t6 to t10 in FIG. 41 and FIG. 42.

As described, in the present exemplary embodiment, current filled in thecapacitor C of the light output compensation unit 20 is applied to theLED units at the LED non-light-emitting intervals according to theexemplary embodiment described above with respect to FIG. 3, so that theLED luminescence apparatus may constantly emit light without generatingnon-light-emitting intervals (LED off intervals).

A subsequent current control operation is performed by repeating theconstant current control performed during the above-described intervalst0 to t8, and thus detailed descriptions thereof will be omitted here.

The present exemplary embodiment has been described such that LEDdriving current increases or decreases in a stepped form by multi-stageconstant current control. However, the present disclosure is not limitedthereto. The waveform of the LED driving current may be modified byvariously setting reference currents for constant current control.

In the present exemplary embodiment, the series-connected LEDs may besequentially driven at constant current using AC voltage, so thatcurrent that increases or decreases in a stepped form can be provided asillustrated in FIG. 41 and FIG. 42, and therefore LED driving currentapproximate to a sinusoidal wave equal to AC voltage is provided,thereby enabling problems related to the power factor, THD, etc. to besolved.

Furthermore, current at each stage is controlled to have constantmagnitude, so that constant driving current can be provided even in theevent of variation in AC voltage (distortion, or increase or decrease inthe magnitude of voltage). Thus, the light output efficiency ofAC-driven LEDs can be improved.

Furthermore, the LED units may be driven at the areas in which LEDs donot emit light due to AC power, by using the current filled in thecapacitor C, so that the LED luminescence apparatus can emit lightduring the entire interval of AC power without generatingnon-light-emitting intervals (LED off intervals).

It will be apparent to those skilled in the art that variousmodifications and variation can be made in the present invention withoutdeparting from the spirit or scope of the invention. Thus, it isintended that the present invention cover the modifications andvariations of this invention provided they come within the scope of theappended claims and their equivalents.

What is claimed is:
 1. A light-emitting diode (LED) driving circuitconfigured to drive LED units, the driving circuit comprising: arectification circuit unit to receive an alternating current (AC) powervoltage and rectify the AC power voltage to output a unidirectionalripple voltage; a pulse-width modulation (PWM) signal generation unit togenerate PWM decision signals; switch units, a first end of each switchunit connected to a cathode of one of the LED units; constant currentcontrol circuit units, a first end of each constant current controlcircuit unit connected to a second end of a respective switch unit, toreceive a current therefrom; and a current control circuit unitconfigured to receive current from the switch units, and generateswitching control signals for the respective switch units tosequentially drive the constant current control circuit units, whereinthe PWM signal generation unit is configured to sequentially drive theLEDs according to the PWM decision signals, and wherein each of theconstant current control circuit units is configured to output a currentcontrol signal to the respective switch unit to control a magnitude ofthe received current to have a specific value.
 2. The LED drivingcircuit of claim 1, wherein each of the current control circuit units isconfigured to generate a respective switching control signal to switch acorresponding switch unit to an open state when downstream stagecurrents are received and any one of the downstream stage currentcomprises a first value.
 3. The LED driving circuit of claim 1, whereinthe PWM signal generation unit further comprises: a frequency detectionunit to detect a frequency of the AC power voltage; a referencefrequency oscillation circuit to oscillate at a reference frequencydifferent from the detected frequency and to generate a referencefrequency signal; a frequency division circuit to divide the referencefrequency signal by a multiple of an integer and to generate afrequency-divided signal; and a PWM output decision unit to decide andoutput the PWM decision signals using the frequency-divided signal. 4.The LED driving circuit of claim 3, wherein the PWM output decision unitis configured to decide the PWM decision signals by logically combiningthe reference frequency signal with the frequency-divided signal.
 5. TheLED driving circuit of claim 4, wherein at least one of the PWM decisionsignals is logically equal to the reference frequency signal.
 6. The LEDdriving circuit of claim 4, wherein at least one of the PWM decisionsignals is equal to logical NOT of the reference frequency signal. 7.The LED driving circuit of claim 4, wherein the PWM decision signalshave a pulse form that repeatedly overlap one another during a cycle ofthe frequency-divided signal.
 8. The LED driving circuit of claim 4,wherein the PWM decision signals have a pulse form that are sequentiallyoutput without overlapping one another.
 9. The LED driving circuit ofclaim 1, wherein the PWM signal generation unit further comprises: afrequency detection unit to detect a frequency of the AC power voltage;a reference frequency oscillation circuit to oscillate at a referencefrequency different from the detected frequency and to generate areference frequency signal; a frequency division circuit to divide thereference frequency signal by a multiple of an integer and to generate afrequency-divided signal; and a PWM output decision unit to decide andoutput the PWM decision signals using the frequency-divided signal. 10.The LED driving circuit of claim 9, wherein the PWM output decision unitis configured to decide the PWM decision signals by logically combiningthe reference frequency signal with the frequency-divided signal. 11.The LED driving circuit of claim 10, wherein the PWM decision signalshave a pulse form that repeatedly overlap one another during a cycle ofthe frequency-divided signal.
 12. The LED driving circuit of claim 9,wherein a total driving current of the LED units has a DC level-shiftedpulse wave form that overlap one another during a cycle of thefrequency-divided signal.
 13. The LED driving circuit of claim 9,wherein the PWM decision signals have a pulse form that are sequentiallyoutput without overlapping one another.
 14. A light-emitting diode (LED)driving circuit, comprising: a rectifier to receive an alternatingcurrent (AC) voltage and rectify the AC voltage to generate a rectifiedvoltage; and a pulse-width modulation (PWM) signal generation unit togenerate a first PWM decision signal and a second PWM decision signal,wherein the PWM signal generation unit is configured to provide thefirst PWM decision signal and the second PWM decision signal to LEDunits, and the PWM signal generation unit is configured to sequentiallydrive the LED units according to the first and the second PWM decisionsignals, and wherein the LED units each comprise a first LED unit and asecond LED unit, and the LED driving circuit further comprises: a firstswitch unit connected to the first LED unit of each LED unit; a firstconstant current controller, the first constant current controllerconfigured to receive a first current from the first switch unit andoutput a first current control signal to the first switch unit tomaintain an amplitude of the first current within a first range; asecond switch unit connected to the second LED unit of each LED unit; asecond constant current controller, the second constant currentcontroller configured to receive a second current from the second switchunit and output a second current control signal to the second switchunit to maintain an amplitude of the second LED unit of each LED unitwithin a second range; and a current control circuit unit to receive thefirst and second currents flowing from the first and second switchunits, and generate a first and second switching control signals toalternately drive the first and second constant current controllers. 15.The LED driving circuit of claim 14, wherein the LED units each comprisea third LED unit, and the LED driving circuit further comprising: athird switch unit connected to the third LED unit of each LED unit; anda third constant current controller, the third constant currentcontroller being configured to receive a third current from the thirdswitch unit and output a third current control signal to the thirdswitch unit to maintain an amplitude of the third LED unit of each LEDunit within a third range.